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Current Electricity MCQs — Physics (page 7)

270 multiple-choice questions on Current Electricity from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

151. Potential difference across a component refers to energy transferred:

  1. from electrical energy to other forms in the component
  2. from chemical energy
  3. to the source
  4. into electrical energy

Answer: A) from electrical energy to other forms in the component

Explanation: Energy given up by charges. SLO P-09-E-16 · Understanding

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152. P = I^2R is derived from P = IV by using:

  1. I = VR
  2. R = IV
  3. V = I^2R
  4. V = IR

Answer: D) V = IR

Explanation: Substitute Ohm's law. SLO P-09-E-12 · Application

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153. A source of e.m.f. 9 V and internal resistance 3 Ω drives a 6 Ω load. The power delivered to the load is:

  1. 12 W
  2. 60 W
  3. 6 W
  4. 3 W

Answer: C) 6 W

Explanation: I = 99 = 1 A; P = I^2R = 6 W. SLO P-09-E-26 · Understanding

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154. Resistors of 5 Ω, 20 Ω are connected in parallel. The combined resistance is:

  1. 40 Ω
  2. 2 Ω
  3. 8 Ω
  4. 4 Ω

Answer: D) 4 Ω

Explanation: 1R = 15 + 120 Rightarrow R = 4 Ω. SLO P-09-E-21 · Application

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155. Resistors of 10 Ω, 20 Ω are in series with a 6 V supply. The current is:

  1. 0.1 A
  2. 0.4 A
  3. 0.2 A
  4. 0.6 A

Answer: C) 0.2 A

Explanation: R = 30 Ω; I = VR = 0.2 A. SLO P-09-E-20 · Application

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156. The formula for resistors in parallel is derived using Kirchhoff's first law and the fact that:

  1. the p.d. across each branch is the same
  2. the p.d.s add
  3. the same current flows in each
  4. the resistances add

Answer: A) the p.d. across each branch is the same

Explanation: I = VR1 + VR2 + ldots SLO P-09-E-21 · Application

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157. Kirchhoff's first law states that at any junction:

  1. the sum of currents entering equals the sum of currents leaving
  2. the voltage is the same everywhere
  3. the sum of e.m.f.s equals the sum of p.d.s
  4. the current is zero

Answer: A) the sum of currents entering equals the sum of currents leaving

Explanation: Current law. SLO P-09-E-18 · Knowledge

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158. Covering an LDR with your hand makes its resistance:

  1. increase
  2. stay the same
  3. become zero
  4. decrease

Answer: A) increase

Explanation: Less light. SLO P-09-E-14 · Knowledge

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159. A cell of e.m.f. 6 V and internal resistance 1 Ω is connected to a 2 Ω resistor. The terminal p.d. is:

  1. 40 V
  2. 2 V
  3. 4 V
  4. 8 V

Answer: C) 4 V

Explanation: I = mathcalER + r = 2 A; V = IR = 4 V (lost volts Ir = 2 V). SLO P-09-E-17 · Understanding

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160. n identical resistors R in series have a combined resistance of:

  1. Rn
  2. n^2R
  3. R
  4. nR

Answer: D) nR

Explanation: Sum of n equal terms. SLO P-09-E-20 · Application

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161. Two resistors in parallel on the same supply: the smaller resistance dissipates:

  1. no power
  2. more power
  3. less power
  4. the same power

Answer: B) more power

Explanation: P = V^2/R with the same V. SLO P-09-E-12 · Application

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162. If the current through a resistor doubles, the power dissipated:

  1. halves
  2. becomes 4 times as large
  3. doubles
  4. is unchanged

Answer: B) becomes 4 times as large

Explanation: P = I^2R. SLO P-09-E-12 · Application

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163. A copper wire has n = 8.5 10^28 m^-3, cross-section 1 10^-6 m^2 and drift velocity 1 10^-4 m/s. The current is (e = 1.6 10^-19 C):

  1. 0.136 A
  2. 2.72 A
  3. 13.6 A
  4. 1.36 A

Answer: D) 1.36 A

Explanation: I = nAvq = 8.5 10^28 1 10^-6 1 10^-4 1.6 10^-19 = 1.36 A. SLO P-09-E-10 · Application

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164. The formula for resistors in series is derived using Kirchhoff's second law and the fact that:

  1. the resistances multiply
  2. the same current flows through each resistor
  3. the currents add
  4. the same p.d. is across each resistor

Answer: B) the same current flows through each resistor

Explanation: V = IR1 + IR2 + ldots SLO P-09-E-20 · Application

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165. Using the wire above, a cell balancing at 75 cm has e.m.f.:

  1. 0.75 V
  2. 1.5 V
  3. 2.67 V
  4. 1.0 V

Answer: B) 1.5 V

Explanation: mathcalE = kl = 2 0.75. SLO P-09-E-23 · Application

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166. If a wire is cut in half, the resistance of each half is:

  1. the same
  2. double
  3. half the original
  4. one quarter

Answer: C) half the original

Explanation: R propto L. SLO P-09-E-13 · Application

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167. The driver cell of a potentiometer must have an e.m.f.:

  1. equal to zero
  2. less than the e.m.f. to be measured
  3. greater than the e.m.f. to be measured
  4. equal to the cell being measured

Answer: C) greater than the e.m.f. to be measured

Explanation: Otherwise no balance point exists. SLO P-09-E-23 · Application

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168. A current of 2 A enters a junction where it splits equally between 4 identical branches. Each branch carries:

  1. 0.25 A
  2. 8 A
  3. 2 A
  4. 0.5 A

Answer: D) 0.5 A

Explanation: 2/4. SLO P-09-E-18 · Knowledge

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169. Increasing the length of a potentiometer wire (same driver p.d.) makes it:

  1. less sensitive
  2. more sensitive (smaller potential gradient)
  3. unable to balance
  4. short-circuited

Answer: B) more sensitive (smaller potential gradient)

Explanation: Each cm corresponds to a smaller p.d. SLO P-09-E-23 · Application

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170. Resistors of 12 Ω, 12 Ω, 12 Ω are connected in parallel. The combined resistance is:

  1. 2 Ω
  2. 40 Ω
  3. 8 Ω
  4. 4 Ω

Answer: D) 4 Ω

Explanation: 1R = 112 + 112 + 112 Rightarrow R = 4 Ω. SLO P-09-E-21 · Application

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171. Resistors of 2 Ω, 3 Ω, 6 Ω are connected in parallel. The combined resistance is:

  1. 0.5 Ω
  2. 1 Ω
  3. 2 Ω
  4. 10 Ω

Answer: B) 1 Ω

Explanation: 1R = 12 + 13 + 16 Rightarrow R = 1 Ω. SLO P-09-E-21 · Application

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172. Which is a source of e.m.f.?

  1. a generator
  2. a fuse
  3. a lamp
  4. a resistor

Answer: A) a generator

Explanation: Converts mechanical to electrical energy. SLO P-09-E-15 · Application

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173. A galvanometer is:

  1. a device that stores charge
  2. a high-voltage source
  3. a sensitive instrument that detects small currents
  4. a resistor

Answer: C) a sensitive instrument that detects small currents

Explanation: Moving-coil meter. SLO P-09-E-24 · Understanding

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174. If one carbon fibre in a parallel network breaks, the total resistance of the network:

  1. increases slightly
  2. becomes infinite
  3. becomes zero
  4. decreases

Answer: A) increases slightly

Explanation: Fewer parallel paths. SLO P-09-E-27 · Understanding

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175. A cell transfers 45 J of energy to 30 C of charge driven round a complete circuit. Its e.m.f. is:

  1. 3 V
  2. 1350 V
  3. 0.75 V
  4. 1.5 V

Answer: D) 1.5 V

Explanation: mathcalE = WQ = 1.5 V. SLO P-09-E-15 · Application

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