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Current Electricity MCQs — Physics (page 9)

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.

201. When a loaded bridge deck bends, the strained carbon fibres show:

  1. a change in mass
  2. a change in colour
  3. no change
  4. a change in resistance

Answer: D) a change in resistance

Explanation: Strain-sensing. SLO P-09-E-27 · Understanding

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202. If the same charge moves through twice the p.d., the energy transferred:

  1. is unchanged
  2. quadruples
  3. doubles
  4. halves

Answer: C) doubles

Explanation: W = QV. SLO P-09-E-11 · Application

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203. In a balanced Wheatstone bridge with P = 10 Ω, Q = 20 Ω, R = 15 Ω, the unknown S is:

  1. 13.3 Ω
  2. 7.5 Ω
  3. 30 Ω
  4. 45 Ω

Answer: C) 30 Ω

Explanation: PQ = RS. SLO P-09-E-22 · Application

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204. The physics principle behind the carbon-fibre method is:

  1. the Doppler effect
  2. Snell's law
  3. resistance depends on length and cross-section of the conducting path (R = rho L/A)
  4. Archimedes' principle

Answer: C) resistance depends on length and cross-section of the conducting path (R = rho L/A)

Explanation: Damage changes the effective L and A. SLO P-09-E-27 · Understanding

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205. In a null method, the galvanometer is used to show:

  1. the resistance
  2. the exact value of a large current
  3. when the current through it is zero
  4. the e.m.f. directly

Answer: C) when the current through it is zero

Explanation: Balance condition. SLO P-09-E-24 · Understanding

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206. Resistivity depends on:

  1. the area of the wire
  2. the material and temperature
  3. the length of the wire
  4. the current

Answer: B) the material and temperature

Explanation: A property of the material. SLO P-09-E-13 · Application

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207. 24 J of energy is transferred when 2 C of charge passes between two points. The p.d. is:

  1. 12 V
  2. 24 V
  3. 48 V
  4. 6 V

Answer: A) 12 V

Explanation: V = WQ = 242 = 12 V. SLO P-09-E-11 · Application

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208. The e.m.f. of a source is equal to the terminal p.d. when:

  1. a large current is drawn
  2. no current is drawn
  3. the circuit is short-circuited
  4. the cell is flat

Answer: B) no current is drawn

Explanation: No internal loss. SLO P-09-E-16 · Understanding

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209. A graph of terminal p.d. V against current I for a cell has a gradient of:

  1. -r
  2. 1r
  3. mathcalE
  4. r

Answer: A) -r

Explanation: V = mathcalE - rI; intercept = e.m.f. SLO P-09-E-17 · Understanding

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210. n identical resistors R in parallel have a combined resistance of:

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

Answer: C) Rn

Explanation: Each adds 1/R. SLO P-09-E-21 · Application

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211. An electron (charge 1.6 10^-19 C) moves through a p.d. of 5 V. The energy transferred is:

  1. 8.0 10^-19 J
  2. 3.1 10^19 J
  3. 5 J
  4. 3.2 10^-20 J

Answer: A) 8.0 10^-19 J

Explanation: W = QV = 1.6 10^-19 5 = 5 eV. SLO P-09-E-11 · Application

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212. Replacing the fixed resistor in a sensing potential divider with a variable resistor allows:

  1. the supply voltage to change
  2. the sensor to work in reverse
  3. the switching point (sensitivity) to be adjusted
  4. zero output always

Answer: C) the switching point (sensitivity) to be adjusted

Explanation: Set the threshold. SLO P-09-E-25 · Understanding

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213. A cell transfers 3 J of energy to 2 C of charge driven round a complete circuit. Its e.m.f. is:

  1. 0.75 V
  2. 3 V
  3. 6 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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214. Thermistors are used in potential dividers to:

  1. provide a p.d. that depends on temperature
  2. store energy
  3. measure current
  4. provide a constant p.d.

Answer: A) provide a p.d. that depends on temperature

Explanation: Temperature sensors. SLO P-09-E-25 · Understanding

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215. Kirchhoff's second law is also called:

  1. Faraday's law
  2. the junction rule
  3. the loop rule
  4. Coulomb's law

Answer: C) the loop rule

Explanation: KVL. SLO P-09-E-19 · Understanding

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216. The short-circuit current of a 1.5 V cell with internal resistance 0.5 Ω is:

  1. 0.33 A
  2. 3 A
  3. 0.75 A
  4. 1.5 A

Answer: B) 3 A

Explanation: I = mathcalE/r. SLO P-09-E-17 · Understanding

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217. Resistors of 2 Ω, 3 Ω, 5 Ω are connected in series. The combined resistance is:

  1. 5 Ω
  2. 100 Ω
  3. 20 Ω
  4. 10 Ω

Answer: D) 10 Ω

Explanation: R = R1 + R2 + ldots = 10 Ω. SLO P-09-E-20 · Application

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218. Starting from V = V1 + V2 with V = IR, V1 = IR1, V2 = IR2, we get:

  1. R = R1R2
  2. 1R = 1R1 + 1R2
  3. R = R1 - R2
  4. R = R1 + R2

Answer: D) R = R1 + R2

Explanation: Divide by I. SLO P-09-E-20 · Application

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219. Resistors of 1 Ω, 2 Ω, 6 Ω are in series with a 9 V supply. The current is:

  1. 2 A
  2. 9 A
  3. 1 A
  4. 0.5 A

Answer: C) 1 A

Explanation: R = 9 Ω; I = VR = 1 A. SLO P-09-E-20 · Application

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220. The unit of e.m.f. is:

  1. newton
  2. ampere
  3. volt
  4. ohm

Answer: C) volt

Explanation: J/C. SLO P-09-E-15 · Application

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221. An ammeter in the main line reads 5 A; ammeters in two of three parallel branches read 1.5 A and 2 A. The third branch reads:

  1. 1.5 A
  2. 0.5 A
  3. 3.5 A
  4. 8.5 A

Answer: A) 1.5 A

Explanation: 5 - 1.5 - 2. SLO P-09-E-18 · Knowledge

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222. When a cell is balanced on a potentiometer, the e.m.f. measured is not affected by its internal resistance because:

  1. the galvanometer cancels it
  2. the wire has no resistance
  3. the driver cell supplies extra p.d.
  4. no current flows through the cell

Answer: D) no current flows through the cell

Explanation: No lost volts at balance. SLO P-09-E-23 · Application

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223. Kirchhoff's first law applies to:

  1. every junction in any circuit
  2. only AC circuits
  3. only series circuits
  4. only batteries

Answer: A) every junction in any circuit

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

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224. Two 10 Ω resistors in parallel are then put in series with a 5 Ω resistor. The total resistance is:

  1. 5 Ω
  2. 15 Ω
  3. 25 Ω
  4. 10 Ω

Answer: D) 10 Ω

Explanation: 5 + 5 = 10 Ω. SLO P-09-E-21 · Application

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225. If cracks form in carbon-fibre-reinforced concrete, the electrical resistance of the fibres:

  1. becomes zero
  2. decreases
  3. stays the same
  4. increases

Answer: D) increases

Explanation: Broken or stretched conducting paths. SLO P-09-E-27 · Understanding

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