Master Current Electricity for Class 12: Key Concepts, MCQs, and Tips for WB Higher Secondary Test

Introduction

Current electricity is one of the most intriguing topics in physics, especially for Class 12 students preparing for the West Bengal Higher Secondary Test. This topic is a cornerstone for understanding the behavior of electric circuits, which finds applications in technology and daily life. Here, we’ll delve deep into the concepts, provide clear explanations, and tackle the most common MCQs to ensure you’re well-prepared.

Understanding Current Electricity

What is Current Electricity?

Current electricity refers to the flow of electric charge through a conductor, typically in the form of electrons. The study involves understanding the concepts of electric potential, resistance, and the effects of current.

Key Characteristics

Electric Current (I): Rate of flow of charge, measured in amperes (A).
Voltage (V): Electric potential difference across a conductor.
Resistance (R): Opposition to the flow of current, measured in ohms (Ω).

Key Concepts of Current Electricity

Ohm's Law

Ohm's Law states that the current passing through a conductor is directly proportional to the voltage across it, provided the temperature remains constant. V=IR

Resistivity and Conductivity

Resistivity ( $\rho$ ): A material property that determines how strongly a material opposes current flow.
Conductivity ( $\sigma$ ): The reciprocal of resistivity, indicating how easily a material conducts electricity.

Series and Parallel Circuits

Series Circuits: Current is the same through all components, but voltage is divided.
Parallel Circuits: Voltage is the same across each component, but current divides.

Kirchhoff’s Laws

Kirchhoff’s Current Law (KCL): The total current entering a junction equals the total current leaving it.
Kirchhoff’s Voltage Law (KVL): The sum of potential differences in a closed loop equals zero.

Electric Power and Energy

Power ( $P$ ) is given by $P = VI = I^2R = \frac{V^2}{R}$ and energy consumed ( $W$ ) is $W = Pt$ .

30+ Important MCQs for WB Higher Secondary Test

Here are common multiple-choice questions to test your understanding:

The SI unit of electric current is:
- A. Volt
- B. Ampere
- C. Ohm
- D. Coulomb
  Answer: B
Ohm’s Law is valid for:
- A. Non-metallic conductors
- B. Superconductors
- C. Metallic conductors
- D. Semi-conductors
  Answer: C
The resistivity of a material depends on:
- A. Length of the conductor
- B. Temperature
- C. Area of cross-section
- D. None of the above
  Answer: B
If two resistors $R_1$ and $R_2$ are connected in series, the total equivalent resistance is:
- A. $R_1 + R_2$
- B. $\frac{R_1 R_2}{R_1 + R_2}$
- C. $R_1 \times R_2$
- D. $R_1 - R_2$
Correct Answer: A
What happens to the resistance of a conductor when its temperature increases?
- A. Decreases
- B. Increases
- C. Remains constant
- D. Becomes zero
  Answer: B

If the length of a conductor is doubled while keeping its cross-sectional area constant, its resistance will:
- A. Remain the same
- B. Double
- C. Halve
- D. Quadruple
  Answer: B
Which instrument is used to measure electric current?
- A. Voltmeter
- B. Ammeter
- C. Galvanometer
- D. Potentiometer
  Answer: B
The reciprocal of resistivity is known as:
- A. Conductance
- B. Conductivity
- C. Resistance
- D. None of the above
  Answer: B
The unit of electric power is:
- A. Watt
- B. Joule
- C. Ampere
- D. Coulomb
  Answer: A
Which material has zero resistivity at very low temperatures?

A. Conductor
B. Semiconductor
C. Superconductor
D. Insulator
Answer: C

Drift velocity is directly proportional to:

A. Resistance
B. Electric Field
C. Resistivity
D. Temperature
Answer: B

In a parallel circuit, if one component fails, the rest of the circuit:

A. Stops working
B. Works normally
C. Becomes overloaded
D. Loses all current
Answer: B

If a wire of resistance $R$ is stretched to double its length, its new resistance becomes:

A. $R$
B. $2 R$
C. $4 R$
D. $\frac{R}{2}$
Answer: C

The temperature coefficient of resistance is:

A. Positive for insulators
B. Negative for semiconductors
C. Positive for metals
D. Both B and C
Answer: D

The current in a circuit is inversely proportional to:

A. Voltage
B. Resistance
C. Power
D. Conductance
Answer: B

The internal resistance of a cell depends on:

A. Temperature
B. Surface area of electrodes
C. Distance between electrodes
D. All of the above
Answer: D

A potentiometer is used to measure:

A. Current
B. EMF
C. Resistance
D. Voltage drop
Answer: B

Which factor does not affect resistance?

A. Material
B. Shape of conductor
C. Current through the conductor
D. Length of conductor
Answer: C

The heating effect of current is given by the equation:

A. $H = I R$
B. H=I²Rt
C. H=V²R
D. $H = IRt$
Answer: B

The drift velocity of electrons is measured in:

A. m/s
B. m/s $^2$
C. Ampere
D. Volt
Answer: A

Electric power is the product of:

A. Current and resistance
B. Current and voltage
C. Voltage and charge
D. Resistance and voltage
Answer: B

If a battery has negligible internal resistance, its terminal voltage is:

A. Zero
B. Equal to its EMF
C. Greater than its EMF
D. Depends on current
Answer: B

The efficiency of an electrical device is given by:

A. $\frac{\text{Input Power}}{\text{Output Power}} \times 100$
B. $\frac{\text{Output Power}}{\text{Input Power}} \times 100$
C. $\frac{\text{Energy Loss}}{\text{Output Power}}$
D. $\text{Output Power} \times \text{Input Power}$
Answer: B

A Wheatstone bridge is used to measure:

A. Resistance
B. Voltage
C. Current
D. Capacitance
Answer: A

The SI unit of conductance is:

A. Siemens
B. Ohm
C. Farad
D. Henry
Answer: A

Which type of resistor is used in a potentiometer?

A. Variable resistor
B. Fixed resistor
C. Light-dependent resistor
D. Thermistor
Answer: A

Superconductors are used in:

A. Electromagnets
B. Transmission lines
C. MRI machines
D. All of the above
Answer: D

Which of the following is not a unit of energy?

A. Joule
B. Kilowatt-hour
C. Electron-volt
D. Ampere
Answer: D

In an ideal conductor, resistance is:

A. Maximum
B. Infinite
C. Zero
D. Constant
Answer: C

The SI unit of capacitance is:

A. Henry
B. Farad
C. Coulomb
D. Tesla
Answer: B

By practicing these MCQs, you’ll have a solid grip on current electricity and improve your chances of acing the West Bengal Higher Secondary Test! For detailed answers and explanations, visit MightyKnowledge .

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Tables and Quick Reference

Formula Table

Concept	Formula
Ohm's Law	$V = IR$
Resistance in Series	$R = R_1 + R_2 + ... + R_n$
Resistance in Parallel	$\frac{1}{R} = \frac{1}{R_1} + \frac{1}{R_2} + ...$
Electric Power	$P = VI = I^2R$
Energy Consumption	$W = Pt$

Comparison Table: Series vs. Parallel Circuits

Property	Series Circuit	Parallel Circuit
Current (I)	Same through all components	Divides among components
Voltage (V)	Divides across components	Same across each component
Resistance (R)	$R = R_1 + R_2$	$\frac{1}{R} = \frac{1}{R_1} + \frac{1}{R_2}$

Conclusion

Mastering the topic of current electricity requires understanding its fundamental principles, solving problems, and practicing MCQs. Use the above concepts and practice questions as your guide to excel in the West Bengal Higher Secondary exam. Keep revising, stay curious, and you’ll surely achieve success!

For more detailed guides and study material, visit MightyKnowledge.

FAQs

What is the principle of Ohm's Law?
Ohm's Law states that $V = IR$ , where voltage is directly proportional to current at constant temperature.

How does temperature affect resistivity?
For conductors, resistivity increases with temperature. For semiconductors, it decreases.

Why is parallel connection preferred in household wiring?
Parallel connections ensure that each device receives the same voltage and continues working even if one fails.

What is the unit of resistivity?
The SI unit of resistivity is ohm-meter ( $\Omega·m$ ).

How to calculate power in an electric circuit?
Power is calculated using $P = VI$ , $P = I^2R$ or $P = \frac{V^2}{R}$

What are superconductors?
Superconductors are materials that exhibit zero resistance below a critical temperature.

Remember, consistent practice and conceptual clarity are key to excelling in physics. Good luck with your preparations!

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