Practice Resistance in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

A measure of how strongly a material opposes electric current, measured in ohms (Ω\Omega) — higher resistance means less current for a given voltage.

Resistance is like friction for electricity — a narrow pipe resists water flow more than a wide one.

Showing a random 20 of 50 problems.

Example 1

challenge
Twelve identical 1 Ω1 \text{ }\Omega resistors are arranged along the edges of a cube. Find the resistance between two opposite corners (body diagonal).

Example 2

medium
A material has resistivity 2×10−8 Ω⋅2\times10^{-8}\,\Omega\cdotm. A wire is 44 m long with cross-section 2×10−62\times10^{-6} m2^2. Find its resistance.

Example 3

easy
If voltage stays constant and resistance triples, the current becomes ___.

Example 4

hard
Find the equivalent resistance between A and B: R1=4 ΩR_1 = 4 \text{ }\Omega in series with the parallel combination of R2=6 ΩR_2 = 6 \text{ }\Omega and (R3=3 ΩR_3 = 3 \text{ }\Omega in series with R4=3 ΩR_4 = 3 \text{ }\Omega).

Example 5

medium
Two resistors 12 Ω12 \text{ }\Omega and 4 Ω4 \text{ }\Omega are in parallel. Find the equivalent resistance.

Example 6

medium
Three identical 9 Ω9 \text{ }\Omega resistors are connected in parallel. Find ReqR_{eq}.

Example 7

medium
A heater draws 10 A10 \text{ A} from a 220 V220 \text{ V} supply. Find its resistance.

Example 8

easy
What is the SI unit of resistance?

Example 9

easy
What is the SI unit of resistance?

Example 10

challenge
A 4 Ω4\,\Omega resistor is in series with a parallel combination of 6 Ω6\,\Omega and 12 Ω12\,\Omega. Find the total resistance.

Example 11

medium
A wire has resistance R=ρLAR = \rho \frac{L}{A}. If you replace a wire with one that is twice as long and has three times the cross-sectional area (same material), how does the resistance change?

Example 12

medium
A wire has resistance 6 Ω6\,\Omega. It is stretched to twice its length (area halves, volume constant). What is the new resistance?

Example 13

easy
A 20 Ω20 \text{ }\Omega resistor and 30 Ω30 \text{ }\Omega resistor are in series. The current through the 20 Ω20 \text{ }\Omega resistor is what fraction of the current through the 30 Ω30 \text{ }\Omega resistor?

Example 14

easy
Two identical resistors are connected in parallel. The equivalent resistance is ___ that of a single resistor.

Example 15

easy
A resistor carries 2 A2 \text{ A} of current when 10 V10 \text{ V} is applied across it. What is the resistance?

Example 16

easy
A bulb labeled 60 W,120 V60 \text{ W}, 120 \text{ V} has what resistance when operating?

Example 17

easy
What is the difference between resistance and resistivity?

Example 18

easy
A resistor has 1212 V across it and 33 A through it. What is its resistance?

Example 19

medium
A wire has length 2 m2 \text{ m}, cross-sectional area 1×10−6 m21 \times 10^{-6} \text{ m}^2, and resistivity ρ=1.7×10−8 Ω⋅m\rho = 1.7 \times 10^{-8} \text{ } \Omega \cdot \text{m} (copper). What is its resistance?

Example 20

medium
Two resistors 6 Ω6\,\Omega and 3 Ω3\,\Omega are in parallel. Find the total resistance.
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