Current Electricity is the study of electric charges in motion. This chapter explains electric current, potential difference, Ohm’s law, resistance, resistivity, and the factors affecting resistance. It also covers series and parallel combinations of resistors, electrical power, and applications of current electricity in daily life.
1. The SI unit of electric current is:
- A. Ampere ✅
- B. Volt
- C. Ohm
- D. Coulomb
Explanation: Electric current is measured in amperes (A), defined as the flow of 1 coulomb of charge per second.
2. Which device is used to measure electric current?
- A. Ammeter ✅
- B. Voltmeter
- C. Ohmmeter
- D. Multimeter
Explanation: An ammeter is connected in series in a circuit to measure current.
3. Ohm’s law is represented by:
- A. V = IR ✅
- B. P = IV
- C. Q = It
- D. R = V/I²
Explanation: Ohm’s law states that voltage is directly proportional to current for a conductor at constant temperature.
4. The SI unit of resistance is:
- A. Ampere
- B. Volt
- C. Ohm ✅
- D. Watt
Explanation: Resistance is measured in ohms (Ω), defined as 1 volt per ampere.
5. Which factor decreases the resistance of a metallic conductor?
- A. Increase in length
- B. Increase in temperature
- C. Increase in cross-sectional area ✅
- D. Use of poor conductors
Explanation: A thicker conductor has more paths for electrons to flow, reducing resistance.
6. In series combination of resistors, the total resistance is:
- A. Sum of individual resistances ✅
- B. Product of individual resistances
- C. Reciprocal of individual resistances
- D. Equal to the smallest resistor
Explanation: For series circuits, R_total = R₁ + R₂ + R₃ …
7. In parallel combination of resistors, the reciprocal of total resistance is:
- A. Sum of reciprocals of individual resistances ✅
- B. Sum of individual resistances
- C. Difference of individual resistances
- D. Product of resistances
Explanation: For parallel circuits, 1/R_total = 1/R₁ + 1/R₂ + 1/R₃ …
8. Electric power is given by the formula:
- A. P = I/R
- B. P = VI ✅
- C. P = IR²
- D. P = V²/R²
Explanation: Power is the rate at which electrical energy is converted to another form, given by P = VI.
9. Which material is commonly used for making resistors?
- A. Copper
- B. Nichrome ✅
- C. Aluminium
- D. Silver
Explanation: Nichrome has high resistivity and low temperature coefficient, making it suitable for resistors.
10. The flow of electric charge per unit time is called:
- A. Electric current ✅
- B. Voltage
- C. Resistance
- D. Power
Explanation: Current measures the rate of flow of electric charge, usually in amperes.
11. Which instrument measures potential difference?
- A. Ammeter
- B. Voltmeter ✅
- C. Galvanometer
- D. Ohmmeter
Explanation: A voltmeter is connected in parallel to measure voltage between two points.
12. Electric energy consumed is given by:
- A. E = IR
- B. E = V/I
- C. E = VIt ✅
- D. E = I²V
Explanation: Energy is the product of voltage, current, and time.
13. What is the unit of electrical energy used in households?
- A. Joule
- B. Kilowatt-hour ✅
- C. Watt
- D. Megawatt
Explanation: 1 kWh = energy consumed by 1 kW appliance running for 1 hour.
14. Which combination of resistors provides the smallest possible resistance?
- A. Series
- B. Parallel ✅
- C. Mixed
- D. Variable
Explanation: Parallel connection allows multiple paths, reducing total resistance.
15. The resistivity of a conductor depends on:
- A. Nature of material ✅
- B. Length of conductor
- C. Cross-sectional area
- D. Voltage applied
Explanation: Resistivity is an intrinsic property determined by the material’s structure.