Practice Ohm's Law in Physics

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

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Quick Recap

The fundamental relationship stating that the voltage (VV) across an ohmic conductor equals the current (II) flowing through it multiplied by its resistance (RR).

More push (voltage) means more flow (current). More resistance means less flow for the same push.

Showing a random 20 of 50 problems.

Example 1

easy
A 12 V12 \text{ V} battery is connected to a 4 Ω4 \text{ } \Omega resistor. What current flows?

Example 2

medium
If the voltage across an ohmic resistor increases by 50%50\%, by what percentage does the current change?

Example 3

medium
What voltage is needed to push 0.25 A0.25 \text{ A} through a 100 Ω100 \text{ } \Omega resistor?

Example 4

challenge
A resistor's voltage and current are measured: (2 V,1 A)(2\text{ V}, 1\text{ A}) and (6 V,2 A)(6\text{ V}, 2\text{ A}). Is this device ohmic?

Example 5

easy
A 1010 V source drives a 5 Ω5\,\Omega resistor. What current flows?

Example 6

hard
A wire of resistance 5 Ω5 \text{ } \Omega is replaced by a wire of the same material with half the length and double the cross-sectional area. What is the new resistance, and what current will it draw at 10 V10 \text{ V}?

Example 7

easy
Sketching VV on the y-axis vs II on the x-axis for an ohmic resistor gives a straight line through the origin. What is its slope?

Example 8

easy
A current of 0.4 A0.4 \text{ A} flows through a 25 Ω25 \text{ } \Omega resistor. What voltage is across it?

Example 9

medium
A 2020 V source feeds a 6 Ω6\,\Omega and 4 Ω4\,\Omega resistor in parallel. What is the total current from the source?

Example 10

medium
In a series circuit, 22 A flows through a 7 Ω7\,\Omega resistor. What is the voltage drop across it?

Example 11

easy
A 1212 V battery is connected to a 4 Ω4\,\Omega resistor. What is the current?

Example 12

medium
Two resistors are tested under the same 12 V12 \text{ V} supply. Resistor A draws 0.6 A0.6 \text{ A}; resistor B draws 1.2 A1.2 \text{ A}. Which has larger resistance, and by what factor?

Example 13

medium
An ammeter reads 250 mA250 \text{ mA} through a resistor when a voltmeter across it reads 5.0 V5.0 \text{ V}. What is the resistance?

Example 14

easy
If voltage across an ohmic resistor doubles, what happens to the current?

Example 15

challenge
An ohmic resistor obeys V=IRV = IR with R=50 ΩR = 50 \text{ } \Omega. A time-varying voltage V(t)=10sin⁡(100t) VV(t) = 10\sin(100 t) \text{ V} is applied. Write I(t)I(t) and find the peak current.

Example 16

easy
Convert before using Ohm's law: a resistor of 22 kΩ\Omega carries 33 mA. What units must you use first?

Example 17

medium
A resistor labelled "5%,100 Ω""5\%, 100 \text{ } \Omega" is connected to a 5 V5 \text{ V} supply. Give the minimum and maximum currents consistent with the tolerance.

Example 18

easy
A 1.5 V1.5 \text{ V} AA cell drives a 30 Ω30 \text{ } \Omega bulb (treat as ohmic). Find the current.

Example 19

easy
Does Ohm's law V=IRV=IR apply exactly to a normal filament light bulb at all currents?

Example 20

easy
A 6 Ω6\,\Omega resistor carries 22 A. What voltage is across it?
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