Class 10 Science: Resistance of a System of Resistors — Practice Questions with Answers
Exam-style CBSE practice questions on Resistance of a System of Resistors (Electricity). Try each one first, then reveal the correct answer and a step-by-step explanation. Free, from EduLevel — the AI teacher for CBSE.
Q1medium1 mark
A wire with resistance R is divided into five identical pieces. These pieces are then connected in a parallel arrangement. If the new equivalent resistance is R', what is the value of the ratio R/R'?
1/25
1/5
5
25
Need a hint?
Consider how the resistance of a single piece relates to the original wire's resistance. Also, recall the formula for calculating the equivalent resistance of components connected in parallel.
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Answer: 25
Explanation: Each of the five pieces has a resistance of R/5. When connected in parallel, the equivalent resistance R' is given by 1/R' = 5/(R/5) = 25/R. Therefore, R' = R/25, and the ratio R/R' is 25.
Q2medium1 markCBSE 2024
Calculate the minimum number of identical bulbs, each rated at 4 V and 6 W, that must be connected in series to operate safely at their intended brightness from a 240 V mains supply.
20
40
60
80
Need a hint?
To operate safely, the total voltage across the series combination of bulbs must equal the mains supply voltage. Consider the voltage rating of each individual bulb.
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Answer: 60
Explanation: In a series connection, the total voltage is the sum of the voltages across each component. To operate safely, each bulb requires 4 V, so the number of bulbs needed is the total supply voltage divided by the voltage per bulb (240 V / 4 V = 60).
Q3easy1 markCBSE 2023
Four identical resistors, each with a resistance of 8 ohms, are connected first in series to obtain an effective resistance R_s. They are then connected in parallel to obtain an effective resistance R_p. What is the value of the ratio R_s / R_p?
32
2
0.5
16
Need a hint?
Recall the formulas for calculating the total resistance when resistors are connected in series and in parallel.
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Answer: 16
Explanation: The total resistance in series (Rs) is n*R = 4 * 8 = 32 Ω. The total resistance in parallel (Rp) is R/n = 8 / 4 = 2 Ω. Therefore, the ratio Rs / Rp is 32 / 2 = 16.
Q4easy1 markCBSE 2020
Calculate the maximum resistance that can be obtained by combining four resistors, each having a resistance of 2 Ω.
2 Ω
1 Ω
2.5 Ω
8 Ω
Need a hint?
To obtain the maximum possible resistance from a combination of resistors, consider how resistors should be connected.
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Answer: 8 Ω
Explanation: Maximum resistance is achieved by connecting all resistors in series. The equivalent resistance is the sum of the individual resistances (2 Ω × 4 = 8 Ω).
Q5easy1 markCBSE 2020
What is the maximum possible resistance that can be achieved by connecting five resistors, each with a resistance of 5 Ω?
1 Ω
5 Ω
10 Ω
25 Ω
Need a hint?
To achieve the maximum possible resistance, consider how resistors should be connected to oppose the flow of current the most.
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Answer: 25 Ω
Explanation: The maximum resistance is obtained when resistors are connected in series. The total resistance in a series combination is the sum of individual resistances (5 Ω × 5 = 25 Ω).
Q6easy1 markCBSE 2020
Two electric bulbs, rated 100 W and 40 W, are connected in a series circuit. If the current flowing through the 100 W bulb is 1 A, what will be the current flowing through the 40 W bulb?
0.4A
0.6A
0.8A
1A
Need a hint?
In a series circuit, the same amount of electric current flows through all the components.
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Answer: 1A
Explanation: In a series circuit, the electric current remains the same through every component. Therefore, the current through the 40 W bulb will be identical to the current through the 100 W bulb, which is 1 A.
Q7easy1 markCBSE 2020
What is the maximum resistance that can be created using four resistors, each with a resistance of 1/2 Ω?
2 Ω
1 Ω
2.5 Ω
8 Ω
Need a hint?
To achieve the maximum possible resistance with a given set of resistors, consider how connecting them in series affects the total resistance compared to connecting them in parallel.
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Answer: 2 Ω
Explanation: To obtain the maximum resistance, the resistors must be connected in series. The total resistance is the sum of the individual resistances (1/2 Ω × 4 = 2 Ω).
Q8easy1 markCBSE 2015, 2013, 2012
What is the minimum possible resistance that can be achieved using five resistors, each with a resistance of 1/5 Ω?
1/5Ω
1/25Ω
1/10Ω
25Ω
Need a hint?
To achieve the minimum possible resistance with multiple resistors, consider how they should be connected.
Show answer & explanation
Answer: 1/25Ω
Explanation: To obtain the minimum equivalent resistance, the resistors must be connected in parallel. The formula for n identical resistors in parallel is Req = R/n, so Req = (1/5)/5 = 1/25 Ω.
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