Unit 1 — Dynamic Electricity and Electromagnetism · Physics. These are 10 questions from the Magmo3 bank on this lesson, from easy to hard. Solve each one, then open "Show answer and explanation". Magmo3 has 85 questions on this lesson, each with an explanation.
Connecting an additional resistor in parallel with an existing combination of resistors causes the equivalent resistance of the whole combination to…
Correct answer: (A) decrease
Explanation: An added parallel branch provides an extra path for the current, lowering the equivalent resistance.
In a parallel combination of resistors connected across a source, which of the following quantities is the same for every resistor?
Correct answer: (C) the potential difference across it
Explanation: All branches of a parallel combination are connected between the same two points, so they share the same potential difference.
Two identical resistors, each of resistance 12 Ω, are connected in parallel. The equivalent resistance of the combination is equal to…
Correct answer: (D) 6 Ω
Explanation: Two equal resistors R in parallel give an equivalent resistance R/2 = 12/2 = 6 Ω.
Three equal resistors, each of resistance R, are available. To obtain the smallest possible equivalent resistance, they should be connected…
Correct answer: (C) all in parallel
Explanation: Connecting all three in parallel gives R/3, the smallest equivalent resistance obtainable from the three resistors.
Two resistors of resistances R and 3R are connected in series. The ratio between the potential difference across R and that across 3R is equal to…
Correct answer: (D) 1/3
Explanation: In series the current is common and V ∝ R, so VR : V_(3R) = 1 : 3.
A 6 Ω resistor and a 3 Ω resistor are connected in parallel across a battery of e.m.f. 12 V (VB) and negligible internal resistance. The total current drawn from the battery is equal to…
Correct answer: (A) 6 A
Explanation: The parallel combination is 2 Ω, so the total current is I = 12/2 = 6 A.
What resistance must be connected in parallel with a 12 Ω resistor so that the equivalent resistance of the combination becomes 4 Ω?
Correct answer: (A) 6 Ω
Explanation: 1/R = 1/4 − 1/12 = 1/6, so R = 6 Ω.
Two batteries are connected in parallel (positive to positive) across a 4 Ω resistor. Battery A has VB = 12 V and battery B has VB = 6 V, and each has an internal resistance of 1 Ω. The current in battery B and its state are…
Correct answer: (D) 2 A, and battery B is being charged
Explanation: With V the common terminal p.d., Kirchhoff's first law gives (12 − V)/1 + (6 − V)/1 = V/4, so V = 8 V. The current through B is (6 − 8)/1 = −2 A: 2 A is forced into B against its e.m.f., so it is being charged.
A total current of 12 A is fed into a parallel combination of three resistors of resistances 2 Ω, 3 Ω and 6 Ω. The current passing through the 3 Ω resistor is equal to…
Correct answer: (A) 4 A
Explanation: The parallel equivalent is 1 Ω, so the common p.d. = 12 × 1 = 12 V and I(3Ω) = 12/3 = 4 A.
A resistor R is connected in parallel with an 8 Ω resistor, and this parallel combination is connected in series with a 6 Ω resistor. If the total equivalent resistance is 10 Ω, the value of R is equal to…
Correct answer: (A) 8 Ω
Explanation: The parallel part = 10 − 6 = 4 Ω, so 1/R = 1/4 − 1/8 = 1/8, giving R = 8 Ω.
The first 10 questions in every subject are free, each with an explanation.