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Physics Practical Class 12 Viva Questions

• Last modified on: 11 months ago
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[PDF] Physics Practical Class 12 Viva Questions

Here you will find viva questions for class 12 physics practicals. Experiment wise viva questions are provided with answers.

• Measurement of Resistance
• To determine resistance per cm of a given wire by plotting a graph of potential difference versus current.
• To find the resistance of a given wire using a metre bridge and hence determine the resistivity (specific resistance) of its material.
• To verify the laws of combination (series) of resistances using a metre bridge.
• To verify the laws of combination (parallel) of resistances using a metre bridge.

2. Measurement of Electromotive Force and Potential Difference

• To compare the EMF of two given primary cells using a potentiometer.
• To determine the internal resistance of a given primary cell using a potentiometer.

3. Galvanometer, Ammeter and Voltmeter

• To determine the resistance of a galvanometer by half-deflection method and to find its figure of merit.
• To convert the given galvanometer (of known resistance and figure of merit) into a voltmeter of desired range and to verify the same.
• To convert the given galvanometer (of known resistance and figure of merit) into an ammeter of desired range and to verify the same.

4. Frequency of AC (Alternating Current) Mains

• To find the frequency of the AC mains with a sonometer.

5. Focal Length of Spherical Mirrors

• To find the value of v for different values of u in the case of a concave mirror and to find the focal length.
• To find the focal length of a convex mirror, using a convex lens.

6. Focal Length of Spherical Lenses

• To find the focal length of a convex lens by plotting graphs between u and v or between 1/u and 1/v.
• To find the focal length of a concave lens using a convex lens.

7. Refractive Index of Prism Material, Glass Slab and Transparent Liquid

• To determine the angle of minimum deviation for a given prism by plotting a graph between the angle of incidence and the angle of deviation.
• To determine the refractive index of a glass slab using a travelling microscope.
• To find the refractive index of a liquid by using a convex lens and plane mirror.

8. Semiconductor Diodes and Transistors

• To draw the I-V characteristic curve of a p-n junction in forward bias and reverse bias.
• To draw the characteristic curve of a Zener diode and to determine its reverse breakdown voltage.
• To study the characteristics of a common emitter npn (or pnp) transistor and to find out the values of current and voltage gains.

In Class 12 physics practical examinations, viva questions plays an important role in evaluating a student’s understanding of the experiments they have performed. These viva questions are designed to assess not only your theoretical knowledge but also your ability to apply that knowledge in a practical setting. Understanding the significance of viva questions and being well-prepared for them can significantly impact your overall score in the practical exams.

Why Are Viva Questions Important in Class 12 Physics Practical?

Viva questions serve as a bridge between theory and practice. They require you to explain the principles behind the experiments you’ve conducted, describe the apparatus used, and elucidate your observations and conclusions. Here’s why viva questions are so crucial:

• In-Depth Understanding: Viva questions demand a deeper understanding of the subject matter. They assess whether you can grasp the concepts beyond just rote memorization.
• Application of Knowledge: They evaluate your ability to apply theoretical knowledge to real-world scenarios. This practical approach is a fundamental aspect of physics.
• Communication Skills: Viva questions assess your communication skills. Can you articulate your thoughts clearly and concisely? Can you explain complex concepts in a simple and coherent manner?
• Critical Thinking: You may encounter unexpected questions during viva sessions. These questions test your ability to think critically and solve problems on the spot.

How to Prepare for the Viva Section in Class 12 Physics Practical

Now that you understand the significance of viva questions, let’s explore how to prepare effectively:

• Comprehensive Revision: Start by revising the theoretical concepts related to the experiments thoroughly. Ensure you can explain these concepts in simple terms.
• Practice Answering: Practice answering viva questions regularly. You can find sample questions in textbooks or online resources. Practice with a partner or a teacher for a realistic simulation.
• Hands-On Experience: Revisit the experiments you’ve performed. Familiarize yourself with the equipment and apparatus used. Understanding the setup and procedure will boost your confidence during the viva.
• Logical Reasoning: Be prepared to provide logical explanations for your observations and results. Understanding the “why” behind the “what” is often a key focus of viva questions.
• Stay Calm and Confident: During the viva, remain calm and composed. If you don’t know the answer to a question, it’s okay to admit it. Confidence in your responses is essential.
• Be Attentive: Listen carefully to the examiner’s questions. Sometimes, they may provide hints or clues within the questions themselves.

viva questions in Class 12 physics practical exams are a means to assess your practical knowledge, problem-solving skills, and communication abilities. By preparing diligently and staying composed during the viva, you can excel in this important aspect of your physics practical examination.

Viva Questions on Graphs and Observations

In this section, we will explore viva questions that often focus on interpreting graphs and explaining observations made during experiments. These questions assess your analytical skills and your ability to draw meaningful conclusions from experimental data.

Interpreting Graphs: Viva Questions and Answers

• A linear graph represents a direct proportionality between two variables. Linearity can be identified by a straight-line relationship between the variables.
• The slope of a distance-time graph represents the speed or velocity of an object. A steeper slope indicates a higher speed.
• In a current-voltage graph for a resistor, the slope represents the resistance (R) of the resistor, according to Ohm’s Law (V = IR).

Addressing Observation-Based Viva Questions

• This observation could be due to factors like the discharge of a capacitor or the change in temperature, affecting the resistance of the circuit.
• This phenomenon occurs because the period of a pendulum is directly proportional to the square root of its length (T ∝ √L), as explained by the pendulum formula.
• Increasing the number of turns in a coil enhances the strength of an electromagnet. This is due to the greater magnetic field produced by the increased current flow through the coil.

These viva questions emphasize your ability to analyze data, draw conclusions, and link observations to underlying physics principles. During your practical exam, be prepared to explain the significance of graphs and provide well-reasoned answers based on your observations, measurements, and experimental outcomes.

Summing Up the Significance of Viva Questions

In your Class 12 physics practical examinations, viva questions serve as a comprehensive assessment tool that goes beyond mere experimentation. They evaluate your understanding of theoretical concepts, your ability to apply knowledge in a laboratory setting, and your communication skills.

Remember, viva questions aren’t designed to catch you off guard or intimidate you. Instead, they aim to gauge your readiness to apply physics principles in real-world scenarios, just as you would in your future scientific endeavors.

Final Tips for Acing Your Physics Practical Viva

• Confidence Is Key: Approach the viva section with confidence. Confidence in your knowledge and preparation can go a long way in demonstrating your competence.
• Thorough Revision: Before the exam, revisit the theoretical concepts related to the experiments you’ve performed. Ensure you can explain these concepts clearly and concisely.
• Practice Makes Perfect: Practice answering viva questions with a partner, teacher, or even in front of a mirror. Practicing helps you refine your answers and build confidence.
• Understand the ‘Why’: When responding to viva questions, don’t just focus on the “what.” Try to explain the “why” behind each step, observation, or result. Understanding the underlying principles is key.
• Stay Composed: If you encounter a challenging question or draw a blank, take a deep breath and remain composed. It’s okay to ask for clarification or admit if you don’t know the answer.
• Be Attentive: Listen carefully to the examiner’s questions. Sometimes, they may provide hints or ask follow-up questions based on your initial response.
• Time Management: Manage your time wisely during the viva. Don’t spend too much time on one question; aim for a balanced distribution of time across all questions.
• Use Proper Terminology: Employ appropriate scientific terminology and units when responding to viva questions. Precision in language can showcase your understanding.
• Stay Neat and Organized: If you need to draw diagrams or sketches, ensure they are neat and well-labeled. A well-organized presentation can make a positive impression.
• Review Your Practical Work: Familiarize yourself with the experiments you’ve conducted. Knowing the setup, apparatus, and procedures can help you answer questions confidently.

Hope this helps!

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Ohm’s Law Practice Problems | Review and Examples

• The Albert Team
• Last Updated On: December 5, 2023

Welcome to the fascinating world of electrical principles, where understanding Ohm’s Law is not just a skill but a necessity. Often considered the backbone of electrical engineering and physics, Ohm’s Law is a fundamental concept that illuminates the relationship between voltage, current, and resistance in an electrical circuit. In this comprehensive guide, we will cover the core of Ohm’s Law, explore its fundamental formula, and work through a series of Ohm’s Law practice problems. Mastering Ohm’s Law is a step towards unraveling the complexities of electronics.

What Does Ohm’s Law State?

Ohm’s Law is a fundamental principle in electronics and physics, providing a simple yet powerful way to understand the relationship between voltage, current, and resistance in electrical circuits. At its core, Ohm’s Law states that the current through a conductor between two points is directly proportional to the voltage across these points and inversely proportional to the resistance between them. This relationship is elegantly captured in the formula V = IR , where V stands for voltage, I for current, and R for resistance.

Understanding Voltage, Current, and Resistance

In order to fully appreciate Ohm’s law, let’s review the three components.

• Voltage (V) : Often described as the electrical force or pressure that drives the flow of electrons through a conductor. It’s the potential difference between two points in a circuit.
• Current (I) : This is the flow of electrical charge, measured in amperes (A). It represents how many electrons are flowing through the circuit.
• Resistance (R) : Resistance is the opposition to the current flow in a circuit. It’s measured in ohms (Ω) and depends on the material, size, and temperature of the conductor.

By manipulating the Ohm’s Law formula, you can solve for any one of these three variables if the other two are known. This makes it an invaluable tool for understanding and designing electrical circuits.

Practical Applications

Ohm’s Law isn’t just a theoretical concept; it has numerous practical applications in everyday life and various industries. Here are a few examples:

• Electronics Design: Engineers use Ohm’s Law to design circuits, select appropriate components, and ensure electrical devices function safely and efficiently.
• Troubleshooting Electrical Problems: Technicians often use Ohm’s Law to diagnose issues in electrical systems, such as finding short circuits or identifying components that are not functioning correctly.
• Educational Purposes: Ohm’s Law is a fundamental concept taught in physics and electronics courses, helping students understand the basics of electrical circuits.
• Power Management: In larger-scale applications like power distribution, Ohm’s Law helps calculate the load that can be safely put on electrical systems without causing damage or inefficiency.

Understanding Ohm’s Law opens up possibilities for creating, managing, and troubleshooting electrical systems, from the smallest electronic devices to large-scale power grids.

What is the Formula for Ohm’s Law?

Ohm’s Law is elegant in its formulation, providing a precise mathematical relationship between voltage, current, and resistance in an electrical circuit.

In the formula for Ohm’s Law, V represents voltage measured in volts (V), I is the current measured in amperes (A), and R is the resistance measured in ohms (Ω). This formula is the cornerstone for analyzing and understanding electrical circuits, requiring two variables to solve.

Ohm’s Law Triangle

The Ohm’s Law triangle is a helpful tool for remembering how to calculate voltage, current, and resistance. It visually represents the formula V=IR in a graphic format, with V at the top, I on the left, and R on the right. By covering the variable you want to calculate, the other two variables show how they relate. For example, covering V shows I\times R , covering I shows /frac{V}{R} , and covering R shows \frac{V}{I} . This tool is handy for beginners and a reference for quick calculations.

Strategies for Solving Ohm’s Law Practice Problems

When solving problems using Ohm’s Law, it’s important to follow a systematic approach:

• Identify Known Quantities: Start by determining which of the three variables (voltage, current, resistance) are known.
• Determine the Unknown: Figure out which variable you need to calculate.
• Use the Ohm’s Law Circle: Utilize the Ohm’s Law circle to understand the relationship between the variables and to choose the correct formula.
• Solve Step-by-Step: Apply the formula and solve for the unknown variable step-by-step, ensuring accuracy in your calculations.
• Check Units: Always check that your units are consistent (volts for voltage, amperes for current, ohms for resistance) and convert if necessary.

By applying these strategies, you can effectively use Ohm’s Law to solve a wide range of electrical problems, enhancing your understanding and skills in electrical theory and practice.

Examples of Ohm’s Law

Calculating Current: If a light bulb has a resistance of 240\text{ ohms} and is connected to a 120\text{-volt} power source, the current flowing through it can be calculated as:

Determining Voltage: For a toaster that draws a current of 5\text{ amperes} and has a resistance of 10\text{ ohms} , the voltage across it is:

Finding Resistance: If a hairdryer operates at 220\text{ volts} and draws a current of 11\text{ amperes} , its resistance is:

These examples demonstrate how Ohm’s Law is applied in practical situations, providing a clear understanding of how electrical components function in various devices.

Ohm’s Law Practice Problems

Here are eight practice problems involving Ohm’s Law, arranged in order of increasing complexity. These problems will help you apply the concepts of voltage, current, and resistance in various scenarios. Work through these on your own, then scroll down for solutions.

1. Basic Current Calculation

A circuit with a 9\text{-volt} battery and a resistor of 3\text{ ohms} . What is the current flowing through the circuit?

2. Resistance Determination

Find the resistance of a bulb that draws 0.5\text{ amperes} from a 120\text{-volt} supply.

3. Voltage Calculation

What is the voltage across a resistor of 15\text{ ohms} through which a current of 2\text{ amperes} is flowing?

4. Multiple Resistors (Series) 

In a series circuit with a 12\text{-volt} battery, if there are two resistors of 4\text{ ohms} and 6\text{ ohms} , what is the current flowing through the circuit?

5. Multiple Resistors (Parallel)

Calculate the total resistance in a parallel circuit with two resistors of 5\text{ ohms} and 10\text{ ohms} . If a voltage of 12\text{-volts} is applied across the circuit, what is the total current flowing through the circuit?

6. Combined Ohm’s Law and Power

A device using 18\text{ watts} of power is connected to a 9\text{-volt} battery. Calculate the current drawn by the device and determine the resistance of the device.

7. Variable Resistance

If the current in a circuit is 0.25\text{ amperes} and the voltage is 10\text{ volts} , what must be the resistance?

8. Complex Circuit Analysis

In a circuit, a 6\text{-ohm} resistor and a 12\text{-ohm} resistor are connected in series to a 9\text{-volt} battery. Calculate the current through each resistor.

Solutions to Ohm’s Law Practice Problems

Are you ready to see how you did? Review below to see the solutions for the Ohm’s Law practice problems.

We have a simple circuit with a 9\text{ V} battery and a 3\ \Omega resistor. In order to solve this, use Ohm’s Law, V=IR to find the current:

Therefore, the current flowing through this circuit is 3\text{ amperes} , typical for small electronic devices.

A bulb is connected to a 120\text{ V} supply and draws 0.5\text{ A} .To find the resistance, rearrange Ohm’s Law to R = V/I :

The bulb has a resistance of 240\ \Omega , indicating it’s suitable for moderate power applications.

A resistor of 15\ \Omega carries a current of 2\text{ A} . Apply V=IR to find the voltage across the resistor:

The voltage across this resistor is 30\text{ V} , typical for small household circuits.

We have a series circuit with a 12\text{ V} battery and two resistors ( 4\ \Omega and 6\ \Omega ). First, sum the resistances in series. Then, apply Ohm’s Law.

Summing the resistance:

Now, apply Ohm’s Law with the total resistance, rearranged for the current:

The current of 1.2\text{ A} flows uniformly through each component in this series circuit.

In this scenario, there is a parallel circuit with two resistors of 5\ \Omega and 10\ \Omega . First, calculate the total resistance in parallel using the reciprocal formula:

Then, apply Ohm’s Law with the total resistance, rearranged for the current:

The total current flowing through the circuit is approximately 3.6\text{ A} .

An 18\text{ W} device is connected to a 9\text{ V} battery. First, find the current using by rearranging the power formula P=VI :

The device draws a current of 2\text{ A} . Next, use Ohm’s Law rearranged for resistance:

The device’s resistance is 4.5\ \Omega .

For a circuit with a current of 0.25\text{ A} and a voltage of 10\text{ V} , apply Ohm’s Law to find the resistance:

The circuit has a resistance of 40\ \Omega , indicating a relatively high resistance for the given current and voltage.

First, calculate the total resistance:

For a series circuit, all elements receive the same current. Each resistor in this series circuit experiences a current of 0.5\text{ A} .

As we reach the end of our exploration into Ohm’s Law, it’s clear that this fundamental principle is more than just a formula; it’s a key to unlocking the mysteries of electrical circuits. Through this guide, we’ve journeyed from the basic understanding of voltage, current, and resistance to applying these concepts in various practical scenarios. The practice problems provided various challenges, from straightforward calculations to more complex circuit analyses, each designed to strengthen your grasp of Ohm’s Law.

Remember, the journey of mastering Ohm’s Law is as much about practice as it is about understanding the theory. Each problem you solve, and each circuit you analyze adds to your skill set, making you more adept at navigating the world of electronics.

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Electronics 

Ohm's law.

Ohm's law is a fundamental equation that shows how voltage, electrical current and electrical resistance are related in simple conductors such as resistors. This experiments allows you to explore Ohm's law and how the coloured bands on resistors codes their resistance. In doing this you will also learn how to use a power supply and 'digital multimeters'.

Press GO to launch the experiment!

• Application
• Quick Guide
• Full Instructions

Ohm’s law

Voltage , current and resistance are the most fundamental quantities for describing the flow of electricity . Ohm’s law shows how these three quantities are related and so is a powerful way of understanding the basic nature of electricity.

This is relevant to vast areas of technology today, including national electricity grids, power generation, design of all electronic devices and all electronic circuits, heating, electrical safety and understanding of natural phenomena such as lightning. This experiment will allow you to explore Ohm’s law by making measurements of voltage, current and resistance.

Resistors are the simplest and most commonly used electronic component and almost all electronic circuits contain them. They can be used to change the properties of any circuit they are part of, such as current flow , how voltage is distributed across components, the speed of a circuit , the amount of amplification from a circuit, the response of a sensor or the amount of electrical heating from a circuit.

The simplest resistors are made of a thin film or wound wire of carbon or metal . They usually have a series of coloured bands that represents both their target resistance value and how much the actual value might vary from this (the ‘ tolerance ’). This experiment lets you practise selecting the appropriate colour bands on a resistor to achieve a certain resistance value.

Digital Multimeters

Digital multimeters (DMMs) are versatile pieces of equipment commonly found in electronics, physics and engineering labs. In this experiment you’ll learn how to use a DMM to measure voltage , current and resistance . You’ll see this piece of equipment in many other FlashyScience experiments!

Use this experiment to find out more!

Download the file below for the quick guide for the  Ohm's Law  experiment (requires login) or follow these brief instructions:

To measure resistance:

• On the right-hand Digital Multimeter (DMM), rotate the switch to resistance measurement.
• Click and drag the clips on the wires attached to the right-hand DMM so that they snap to the wires either side of the resistor (make sure the power supply is turned off).
• Note the resistance value shown on the DMM screen.

To change the resistor:

• Click the resistor you wish to change to move to the  Selection  screen.
• Click on the colour band you wish to change.
• Click on the palette colour you wish to select.
• Click on the resistor wire to return to the main screen.

To use voltage and current:

• Turn on the power supply (right hand side of screen) and turn the dial to set the voltage.
• To measure  current through the resistor  – turn the  left-hand DMM  dial to DC current.
• To measure the  voltage across the resistor  – turn the  right-hand DMM  dial to DC voltage.
• NOTE: in this experiment the power supply voltage is also shown directly on its display.

​Download the file below for full instructions for the Ohm's Law  experiment (requires log in).

Download the files below for activities for the Ohm's Law  experiment (requires login).

• ACTIVITY 1: Investigate what the different coloured bands on resistors mean
• ACTIVITY 2: Learn how to use a DMM to measure electrical resistance
• ACTIVITY 3: Explore the effect of the tolerance band (band 4) on resistors
• ACTIVITY 4: Explore the statistics of resistance values from resistors with the same band colour coding
• ACTIVITY 5: Investigate Ohm’s law by measurement of voltage and current with a resistor
• ACTIVITY 6: Investigate Ohm’s law by measurement of current for different resistors with a fixed voltage
• ACTIVITY 7: Investigate Ohm’s law by measurement of voltage for different resistors with a constant current
• ACTIVITY 8: Investigate the power consumption due to electricity flowing in a single resistor
• ACTIVITY 9: Investigate the power consumption due to electricity flowing through different resistances

(Available as separate downloads or all activities)

*NEW* Now also available in editable Microsoft Word format

Download the file below for the background science behind the Ohm's Law  experiment (requires log in).

Potential Divider

A potential divider is a simple circuit that uses resistors to supply a variable 'potential difference' (i.e. voltage).This can be used for many applications, including control of temperature in a fridge or as audio volume controls. Understanding how the resistors in the circuit allow this is important for designing many electronic circuits. Here you can investigate how changes in the two resistors can lead to different voltages across them. 

Most electrical or electronic circuits use the voltage across the circuit components to perform some task. This includes motors, sensors, speakers, computer chips, LEDs and diode lasers, communications antennas (e.g. in mobile phones), heaters, turbines, and mains electricity delivery to houses and industry.

It is important to know how to control the voltages in these circuits to make the applications work! The simplest circuit to start to understand this is the  potential divider , which is made up of two resistors in series . Other circuits may be made of more advanced components but often use the same principles of voltage (i.e. ‘potential’) division. For example: two  transistors  in opposite high or low resistance states and connected in series are used to define whether a ‘ logic gate ’ is set to a digital ( Boolean ) value of 1 or 0, and are a fundamental building block of how a digital computer processor works.

Sensors can be made from a fixed resistor and a component that has a resistance that depends on whatever is being sensed connected, e.g. a  thermistor  for sensing heat or a  light-dependent resistor  for sensing light. A voltage applied to the two components in series allows the voltage across the fixed resistor to be a measure of the resistance of the sensing element’s resistance. This approach can avoid some difficulties of just using the single element, such as high power consumption.

Electrical heaters (including room heaters, cookers and hair dryers) use a fixed resistance   heating element  (e.g. a coil of wire) and a variable resistance   transistor  in series. The resistance of the transistor then controls how much voltage is across the heating element and, therefore, how much electrical heating is produced!

This experiment allows you to gain a good understanding of the  potential  divider . It also allows you to reinforce your understanding of  Ohm’s law , how  resistor  coloured bands code for resistance, and how to use  digital multimeters  (DMMs), which you may have already met in the FlashyScience  Ohm’s L aw  experiment.

​Download the file below for the quick guide for the  Potential Divider  experiment (requires login) or follow these brief instructions:

• On the right-hand Digital Multimeter (DMM) rotate the switch to resistance measurement.
• Click and drag the clips on the wires attached to the right-hand DMM so that they snap to the wires either side of either or both resistors (make sure the power supply is turned off).

To change a resistor:

To measure voltage and current:

• NOTE: the output voltage of the power supply is also shown on its display.

Download the file below for full instructions for the Potential Divider  experiment (requires log in).

Download the file below for activities for the Potential Divider  experiment (requires login).

• ACTIVITY 1: Investigate how the resistances of resistors in series combine
• ACTIVITY 2: Investigate how the current in a potential divider is controlled
• ACTIVITY 3: Explore how voltage in a potential divider depends on the resistor values
• ACTIVITY 4: Consider the voltage ratios across resistors in a potential divider
• ACTIVITY 5: Achieve certain voltages by changing the resistor values
• ACTIVITY 6: Explore power consumption in a potential divider
• ACTIVITY 7: Achieving particular property values in potential dividers
• ACTIVITY 8: Design a potential divider heating element
• ACTIVITY 9: Design a volume control element
• ACTIVITY 10: Design a sensor circuit

Download the file below for the background science behind the Potential Divider  experiment (requires log in).

Resistivity of a Wire

The electrical resistivity of a wire tells us how well the wire material conducts electricity. This is crucial information for any application that involves conducting electricity, including wind turbines, electric vehicles, household electrical goods and computers. Here you can measure the resistivity of wires of different materials and widths, and consider which would be best suited for conducting electricity.

Electronic materials are crucial to our life today , and electrical ‘resistivity’ tells us how good or poor a material is at conducting electricity.

We use materials with low electrical resistivity to transmit electrical power from generators, across grid distribution networks , and to homes and workplaces for use . Designers of electrical devices rely on knowing the resistivity of wire used in order to calculate the resistance of components.

These devices range in size from enormous machines such as wind turbines or industrial lifting equipment ; motors or engines in electric vehicles and all-new electric aircraft ; consumer products such as washing machines, hair dryers and ovens ; and the nanoscale components within the computer chips found in smart devices, laptops, and mobile phones .  

In fact, modern computing is based on controlling the resistivity of semiconductor materials in a type of transistor (known as ‘field effect transistors’ using ‘CMOS’ technology).

Measuring electrical resistivity helps us to understand the properties of materials, to monitor manufacturing processes, and to select the best material for an application.

Download the file below for the quick guide for the  Resistivity of a Wire  experiment (requires login) or follow these brief instructions:

• Click on the right hand wire post to move to the  Select Wire  screen.
• Open the micrometer by dragging the thumbwheel down.
• Choose a material and drag the unlabelled wire into the micrometer.
• Close the micrometer and measure the wire's width.
• Click on the wire while it's in the micrometer to return to the  main screen .
• Click on the switch to turn it on.
• Measure voltage and current for a variety of contact positions on the wire.
• Calculate resistance for each contact position. 
• Plot resistance vs contact position and calculate the gradient of a line of best fit.
• Multiply the line's gradient by the wire's cross-sectional area to obtain the wire's electrical resistivity.

Download the file below for full instructions for the Resistivity of a Wire  experiment (requires log in).

Download the file below for activities for the Resitivity of a Wire  experiment (requires login).

• QUICK ACTIVITIES: 5 quick activities to try
• ACTIVITY 1: Different wire lengths

(Available as separate downloads or all activities)

Download the file below for the background science behind the Resitivity of a Wire  experiment (requires log in).

IV Characteristics of Devices

An 'IV characteristic' of a device shows how the electrical current in the device changes with applied potential difference. The IV characteristic is linear for some devices and nonlinear for others. This experiment allows you to explore the IV characteristics of resistors, a filament lamp and diodes by changing and measuring potential difference and current. 

Electricity powers the modern world. It is essential for electronic devices, home appliances, travel and school, work and leisure.

The widespread use of electricity is because we can make so many components that have different electrical behaviours, and then combine them to make all sorts of devices and machines. These behaviours can be seen most easily by creating a graph of the electrical current ( I ) through a component against the potential difference ( V ) placed across it. This graph is known as a component’s IV characteristic .

The simplest component is the electrical resistor . These have fixed electrical resistance , which means the electrical current is proportional to the potential difference and the IV characteristic is linear . Resistors are vital to almost all electrical devices, from a mobile phone to the world’s most powerful supercomputer, a flashlight to electric vehicles, an electric toothbrush to a medical scanner, your internet router to a communications satellite, or a vacuum cleaner to air-conditioning.

Diodes  are made of two different semiconductor materials joined together and only allow electricity to flow in one direcion through them. They are hugely important in electronics and electrical engineering. They are most often used to convert alternating current (AC) electricity to direct current (DC), for example to convert mains electricity into 12 V DC used for charging mobile devices. They are also widely used to protect electronic circuits by preventing unwanted currents. 

Filament lamps might not be used for lighting as much as they once were but they show interesting electrical effects. They contain a long, thin metal 'filament' that heats up when high electrical current is flowing, which results in it starting to glow and give off light. The heating also changes the filament's electrical resistance, which results in a non-linear IV characteristic .

This virtual experiment will allow you to explore the electrical behaviour of resistors, diodes and filament lamps. You can take measurements of current and potential difference, plot a graph of their IV characteristics, and find their resistance values .

Download the file below for the quick guide for the IV Characteristics of Devices  experiment (requires login).

Download the file below for full instructions for the IV Characteristics of Devices  experiment (requires log in).

Download the files below for activities for the IV Characteristics of Devices  experiment (requires login).

• ACTIVITY 1: IV characteristics of resistors
• ACTIVITY 2: IV characteristic of a filament lamp
• ACTIVITY 3: IV characteristic of a diode
• ACTIVITY 4: Power consumption of resistors (advanced)
• ACTIVITY 5: Power consumption of  a filament lamp (advanced)

(Available as separate downloads or all activities)

Download the file below for the background science behind the IV Characteristics of Devices experiment (requires log in).

Resistance (of a wire)

Understanding the electric resistance of metal wires is fundamental to being able to design electrical machines and electronic devices. In this experiment, you can vary the effective length of a wire by moving an electrical contact and then go on to measure the wire's electric resistance by measuring potential difference and electric current on analogue dials. 

Electricity powers so much of our life today. We use metal wires to transmit electrical power from power generators, such as power stations, ‘PV’ (photovoltaic) devices and wind turbines, to our homes and workplaces.

We use ‘ resistance ’ to measure how easily materials allow electrical current to flow. It is vital to the design of power distribution networks over long distances to understand how the length of a metal wire affects its resistance.

On smaller scales, it is important to know how the length of a conducting wire changes its resistance for applications that use motors , from washing machines through to electric cars and industrial machines . Electricity is also used in heaters , from industrial furnaces for large-scale materials processing through to ovens, underfloor heating and kettles, and in all sorts of electronic devices , such as computers , screens and sensors .

Designing any of these applications to be efficient and effective requires understanding how electricity flows through the materials in the various devices.

Download the file below for the quick guide for the Resistance (of a wire)  experiment (requires login).

Download the file below for full instructions for the Resistance (of a wire)  experiment (requires log in).

Download the files below for activities and associated worksheets for the Resistance (of a wire ) experiment (requires login).

• ACTIVITY 1: Effect of wire length on its resistance
• ACTIVITY 2: Effect of wire width on its resistance
• ACTIVITY 3: The resistance of different materials

(Available as separate downloads or all activities/all worksheets)

Download the file below for the background science behind the Resitance (of a wire) experiment (requires log in).

• Current Electricity

Ohm’s law states the relationship between electric current and potential difference. The current that flows through most conductors is directly proportional to the voltage applied to it. Georg Simon Ohm, a German physicist was the first to verify Ohm’s law experimentally.

Ohm’s Law Explanation

One of the most basic and important laws of electric circuits is Ohm’s law.

Ohm’s law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperatures remain constant.

Mathematically, this current-voltage relationship is written as,

In the equation, the constant of proportionality, R, is called Resistance and has units of ohms, with the symbol Ω.

The same formula can be rewritten in order to calculate the current and resistance respectively as follows:

Ohm’s law only holds true if the provided temperature and the other physical factors remain constant. In certain components, increasing the current raises the temperature . An example of this is the filament of a light bulb, in which the temperature rises as the current is increased. In this case, Ohm’s law cannot be applied. The lightbulb filament violates Ohm’s Law .

Relationship Between Voltage, Current and Resistance

Water Pipe Analogy for Ohm’s Law

Ohm’s Law describes the current flow through a resistance when different electric potentials (voltage) are applied at each end of the resistance . Since we can’t see electrons, the water-pipe analogy helps us understand the electric circuits better. Water flowing through pipes is a good mechanical system that is analogous to an electrical circuit.

Here, the voltage is analogous to water pressure, the current is the amount of water flowing through the pipe, and the resistance is the size of the pipe. More water will flow through the pipe (current) when more pressure is applied (voltage) and the bigger the pipe (lower the resistance).

The video below shows the physical demonstration of the Waterpipe analogy and explains to you the factors that affect the flow of current

Experimental Verification of Ohm’s Law

Ohm’s Law can be easily verified by the following experiment:

Apparatus Required:

• Initially, the key K is closed and the rheostat is adjusted to get the minimum reading in ammeter A and voltmeter V.
• The current in the circuit is increased gradually by moving the sliding terminal of the rheostat. During the process, the current flowing in the circuit and the corresponding value of potential difference across the resistance wire R are recorded.
• This way different sets of values of voltage and current are obtained.
• For each set of values of V and I, the ratio of V/I is calculated.
• When you calculate the ratio V/I for each case, you will come to notice that it is almost the same. So V/I = R, which is a constant.
• Plot a graph of the current against the potential difference, it will be a straight line. This shows that the current is proportional to the potential difference.

Similar Reading:

• Kirchhoff’s Law
• Faraday’s Laws
• Laws of Thermodynamics

Ohm’s Law Magic Triangle

Ohm’s Law Solved Problems

Example 1: If the resistance of an electric iron is 50 Ω and a current of 3.2 A flows through the resistance. Find the voltage between two points.

If we are asked to calculate the value of voltage with the value of current and resistance, then cover V in the triangle. Now, we are left with I and R or more precisely I × R.

Therefore, we use the following formula to calculate the value of V:

Substituting the values in the equation, we get

V = 3.2 A × 50 Ω = 160 V

Example 2: An EMF source of 8.0 V is connected to a purely resistive electrical appliance (a light bulb). An electric current of 2.0 A flows through it. Consider the conducting wires to be resistance-free. Calculate the resistance offered by the electrical appliance.

When we are asked to determine the value of resistance when the values of voltage and current are given, we cover R in the triangle. This leaves us with only V and I, more precisely V ÷ I.

R = 8 V ÷ 2 A = 4 Ω

Calculating Electrical Power Using Ohm’s Law

The rate at which energy is converted from the electrical energy of the moving charges to some other form of energy like mechanical energy, heat energy, energy stored in magnetic fields or electric fields, is known as electric power. The unit of power is the watt. The electrical power can be calculated using Ohm’s law and by substituting the values of voltage, current and resistance.

Formula to find power

What is a Power Triangle?

The power triangle can be employed to determine the value of electric power, voltage and current when the values of the other two parameters are given to us. In the power triangle, the power (P) is on the top and current (I) and voltage (V) are at the bottom.

Ohm’s Law Pie Chart

Ohm’s Law Matrix Table

Ohm’s Law Applications

The main applications of Ohm’s law are:

• To determine the voltage, resistance or current of an electric circuit.
• Ohm’s law maintains the desired voltage drop across the electronic components.
• Ohm’s law is also used in DC ammeter and other DC shunts to divert the current.

Limitations of Ohm’s Law

Following are the limitations of Ohm’s law:

• Ohm’s law is not applicable for unilateral electrical elements like diodes and transistors as they allow the current to flow through in one direction only.
• For non-linear electrical elements with parameters like capacitance, resistance etc the ratio ofvoltage and current won’t be constant with respect to time making it difficult to use Ohm’s law.

The video about conductance, resistance, and ohm’s law

Frequently Asked Questions – FAQs

What does ohm’s law state.

Ohm’s law states that the current through a conductor between two points is directly proportional to the voltage across the two points.

What can Ohm’s law be used for?

Ohm’s law is used to validate the static values of circuit components such as current levels, voltage supplies, and voltage drops.

Is Ohm’s law Universal?

No. Ohm’s law is not a universal law. This is because Ohm’s law is only applicable to ohmic conductors such as iron and copper but is not applicable to non-ohmic conductors such as semiconductors.

Why is Ohm’s law not applicable to semiconductors?

Ohm’s law doesn’t apply to semiconducting devices because they are nonlinear devices. This means that the ratio of voltage to current doesn’t remain constant for variations in voltage.

When does Ohm’s law fail?

Ohm’s law fails to explain the behaviour of semiconductors and unilateral devices such as diodes. Ohm’s law may not give the desired results if the physical conditions such as temperature or pressure are not kept constant.

Watch the video and solve important questions in the chapter Electricity Class 10

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

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