Chapter 12: Electricity
Here is the compilation of all intext and exercise questions from Chapter 12: Electricity (Class 10 NCERT Science textbook):
Intext Questions
Page 215:
- What is the relationship between the current flowing through a conductor and the potential difference across its ends?
- What is the purpose of an electric circuit?
Page 218:
3. What do you mean by electrical resistance?
4. Why do we use an ammeter to measure current in a circuit and a voltmeter to measure potential difference?
Page 220:
5. What happens to the current when the resistance in a circuit is increased, assuming the potential difference remains constant?
6. Why are electric bulbs rated in watts?
Exercise Questions
Page 221-222:
Define the term electric current.
What is the unit of electric current?
What is the relationship between voltage, current, and resistance?
State Ohm’s Law.
What is meant by the resistance of a conductor? How does it depend on its length and cross-sectional area?
What happens to the resistance of a conductor when its length is doubled?
A 6-ohm resistor is connected in series with a 12-ohm resistor. What is the total resistance of the combination?
Why is copper used as a wire in electrical circuits?
How can we increase the resistance of a conductor?
Calculate the resistance of a wire of length 2 m and cross-sectional area 1 mm². The resistivity of the material is 1.5×10−7Ωm.
Page 222-223:
A current of 3 A flows through a conductor for 5 minutes. What is the amount of charge passing through the conductor?
What do you understand by the term "power of an electric current"? What is the SI unit of power?
Calculate the power consumed by a 100 W electric bulb when it is used for 2 hours.
What is the total resistance of two resistors, 6 ohms and 12 ohms, connected in parallel?
What is the formula for calculating the total resistance of resistors in parallel?
Explain the difference between series and parallel combinations of resistors.
Exercise Questions
Page 234-235:
State the magnetic effect of electric current.
What is the use of a solenoid?
Describe an activity to demonstrate the magnetic field around a current-carrying conductor.
What is an electromagnet? How can the strength of an electromagnet be increased?
Why is a solenoid used in an electric bell?
State Fleming’s left-hand rule and give its application.
What is the function of a galvanometer?
Explain how a current-carrying conductor placed in a magnetic field experiences a force.
What are the factors on which the force experienced by a current-carrying conductor in a magnetic field depends?
Here are the answers to your questions:
Conceptual Questions:
1. Relationship between Current and Potential Difference
The current flowing through a conductor is directly proportional to the potential difference (voltage) across its ends, provided the temperature and other physical conditions remain constant. This is stated by Ohm’s Law:
V = IR
2. Purpose of an Electric Circuit
An electric circuit provides a closed path for the flow of electric current, allowing electrical energy to be transferred from a source (like a battery) to different components (like bulbs, fans, etc.).
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Page 218 Questions:
3. Meaning of Electrical Resistance
Electrical resistance () is the property of a conductor that opposes the flow of electric current. It is measured in ohms (Ω) and depends on the material, length, cross-sectional area, and temperature of the conductor.
4. Why Use an Ammeter for Current and a Voltmeter for Potential Difference?
An ammeter measures current and is connected in series because it has very low resistance, allowing maximum current to pass through.
A voltmeter measures potential difference and is connected in parallel across a component because it has very high resistance, preventing it from affecting the circuit.
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Page 220 Questions:
5. Effect of Increasing Resistance on Current (Constant Potential Difference)
According to Ohm’s Law , if resistance () increases while voltage () remains constant, the current () decreases.
6. Why Are Electric Bulbs Rated in Watts?
Electric bulbs are rated in watts (W) because power consumption depends on both voltage and current. Power is given by:
P = VI = I^2 R
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Exercise Questions (Page 221-222):
1. Definition of Electric Current
Electric current is the flow of electric charge (electrons) through a conductor per unit time. It is denoted by and measured in amperes (A).
2. Unit of Electric Current
The unit of electric current is ampere (A).
ampere = coulomb per second (1 A = 1 C/s).
3. Relationship Between Voltage, Current, and Resistance
The relationship is given by Ohm’s Law:
V = IR
4. Statement of Ohm’s Law
Ohm’s Law states that the current () through a conductor is directly proportional to the voltage () across its ends and inversely proportional to its resistance (), provided the temperature remains constant:
V = IR
5. Meaning of Resistance and Its Dependence on Length & Area
Resistance R is the property that resists the flow of current. It depends on:
Length and cross section area
Resistance is **inversely proportional** to the area. A thicker wire has lower resistance.
6. Effect on Resistance When Length Is Doubled
Since , if the length is doubled, resistance will also double.
7. Total Resistance in Series (6Ω + 12Ω)
In a series circuit, total resistance is the sum of individual resistances:
R_{\text{total}} = R_1 + R_2 = 6Ω + 12Ω = 18Ω
8. Why Is Copper Used in Electrical Wiring?
Copper is used because:
It has low resistance, allowing efficient current flow.
It is ductile and flexible, making it easy to use.
It is highly conductive, reducing energy loss.
9. How to Increase the Resistance of a Conductor?
Resistance can be increased by:
Increasing the length of the conductor.
Decreasing the cross-sectional area (using a thinner wire).
Using a material with higher resistivity (like nichrome instead of copper).
Increasing the temperature, as resistance generally increases with heat in metallic conductors.
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