High School Physics : Electric Circuits

Study concepts, example questions & explanations for High School Physics

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Example Questions

Example Question #1 : Electricity And Magnetism

What is the voltage of a circuit with \displaystyle 10A of current and \displaystyle 20\Omega of resistance?

Possible Answers:

\displaystyle 10V

\displaystyle 30V

\displaystyle 0.5V

\displaystyle 200V

\displaystyle 2V

Correct answer:

\displaystyle 200V

Explanation:

For this problem, use Ohm's law: \displaystyle V=IR. In this equation \displaystyle V is the voltage, \displaystyle I is the current, and \displaystyle R is the resistance.

Plug in the given values and solve for the voltage.

\displaystyle V=10A* 20\Omega

\displaystyle V=200V

Example Question #2 : Electricity And Magnetism

What is the current of a circuit with a voltage of \displaystyle 12V and a total resistance of \displaystyle 5\Omega?

Possible Answers:

\displaystyle 60A

\displaystyle 0.42A

\displaystyle 7A

\displaystyle 4.8A

\displaystyle 2.4A

Correct answer:

\displaystyle 2.4A

Explanation:

For this problem, use Ohm's law: \displaystyle V=IR . In this equation \displaystyle V is the voltage, \displaystyle I is the current, and \displaystyle R is the resistance.

We can re-arrange the equation to solve specifically for \displaystyle I.

\displaystyle \frac{V}{R}=I

Plug in the given values for voltage and resistance to solve for the current.

\displaystyle \frac{V}{R}=I

\displaystyle \frac{12V}{5\Omega}=I

\displaystyle 2.4A=I

Example Question #1 : Circuit Calculations And Concepts

What is the resistance in a circuit with a voltage of \displaystyle 50V and a current of \displaystyle 8A?

Possible Answers:

\displaystyle 6.25\Omega

\displaystyle 58\Omega

\displaystyle 0.16\Omega

\displaystyle 400\Omega

\displaystyle 42\Omega

Correct answer:

\displaystyle 6.25\Omega

Explanation:

For this problem, use Ohm's law: \displaystyle V=IR . In this equation \displaystyle V is the voltage, \displaystyle I is the current, and \displaystyle R is the resistance.

We can re-arrange the equation to solve specifically for \displaystyle R.

\displaystyle \frac{V}{I}=R

Plug in the given values for voltage and current and solve for resistance.

\displaystyle \frac{V}{I}=R

\displaystyle \frac{50V}{8A}=R

\displaystyle 6.25\Omega=R

Example Question #1 : Circuit Calculations And Concepts

\displaystyle 9V battery is connected to a circuit. The measured current is \displaystyle 2A. What is the equivalent resistance?

Possible Answers:

\displaystyle 10\Omega

\displaystyle 4.5\Omega

\displaystyle 18\Omega

\displaystyle 9\Omega

\displaystyle 0.22\Omega

Correct answer:

\displaystyle 4.5\Omega

Explanation:

For this problem, use Ohm's law: \displaystyle V=IR

We are given the voltage and current, allowing us to solve for the resistance.

\displaystyle 9V=2A* R

\displaystyle \frac{9V}{2A}=R

\displaystyle 4.5\Omega=R

Example Question #3 : Electricity And Magnetism

A closed electric circuit is set up so that there is a current of \displaystyle 9.9A and a voltage of \displaystyle 30.22V. What is the resistance in the circuit?

Possible Answers:

\displaystyle 20.32\Omega

\displaystyle 299.18\Omega

\displaystyle 0.33\Omega

\displaystyle 3.05\Omega

\displaystyle 6.1\Omega

Correct answer:

\displaystyle 3.05\Omega

Explanation:

For this problem, use Ohm's law: \displaystyle V=IR.

We are given the current and the voltage. Using these terms, we can solve for the resistance.

\displaystyle V=IR

\displaystyle 30.22V=(9.9A) R

\displaystyle \frac{30.22V}{9.9A}=R

\displaystyle 3.05\Omega=R

Example Question #1 : Electric Circuits

The current in a circuit is \displaystyle 20A. If the voltage is \displaystyle 35V, what is the total resistance?

Possible Answers:

\displaystyle 70\Omega

\displaystyle 3.5\Omega

\displaystyle 0.57\Omega

\displaystyle 700\Omega

\displaystyle 1.75\Omega

Correct answer:

\displaystyle 1.75\Omega

Explanation:

For this problem use Ohm's law:

\displaystyle V=IR

We are given the current and the voltage, allowing us to solve for the resistance.

\displaystyle 35V=(20A)*R

\displaystyle R=\frac{35V}{20A}

\displaystyle R=1.75\Omega

Example Question #3 : Electric Circuits

An electrical circuit has a total of \displaystyle 3.22\Omega resistance and \displaystyle 8V. What is the current?

Possible Answers:

\displaystyle 0.403A

\displaystyle 2.48A

\displaystyle 11.22A

\displaystyle 25.76A

\displaystyle 0.089A

Correct answer:

\displaystyle 2.48A

Explanation:

For this problem use Ohm's law:

\displaystyle V=IR

We are given the resistance and the voltage, allowing us to solve for the current.

\displaystyle 8V=I*(3.22\Omega)

\displaystyle I=\frac{8V}{3.22\Omega}

\displaystyle I=2.48A

Example Question #2 : Electric Circuits

An electrical circuit has a current of \displaystyle 8A and \displaystyle 32\Omega of resistance. What is the voltage?

Possible Answers:

\displaystyle 4V

\displaystyle 128V

\displaystyle 256V

\displaystyle 0.25V

\displaystyle 40V

Correct answer:

\displaystyle 256V

Explanation:

For this problem use Ohm's law:

\displaystyle V=IR

We are given the resistance and the current, allowing us to solve for the voltage.

\displaystyle V=(8A)(32\Omega)

\displaystyle V=256V

Example Question #3 : Electric Circuits

An electrical circuit has a current of \displaystyle 13A and \displaystyle 26\Omega of resistance. What is the voltage?

Possible Answers:

\displaystyle 338V

\displaystyle 2V

\displaystyle 13V

\displaystyle 39V

\displaystyle 0.5V

Correct answer:

\displaystyle 338V

Explanation:

For this problem use Ohm's law:

\displaystyle V=IR

We are given the resistance and the current, allowing us to solve for the voltage.

\displaystyle V=(13A)(26\Omega)

\displaystyle V=338V

Example Question #2 : Circuit Calculations And Concepts

A circuit has a current, \displaystyle I, a voltage, \displaystyle V, and a resistance, \displaystyle R. If the voltage remains constant, but the current is doubled (\displaystyle 2I), what must the new resistance be?

Possible Answers:

\displaystyle \frac{1}{4}R

\displaystyle 4R

\displaystyle 2R

There is insufficient information to solve

\displaystyle \frac{1}{2}R

Correct answer:

\displaystyle \frac{1}{2}R

Explanation:

To solve this problem, use Ohm's law:

\displaystyle V=IR

Since we are doubling the current, but the voltage is remaining the same, we can set our old and new equations equal to each other.

\displaystyle I_1R_1=V=I_2R_2

We know that the second current is equal to twice the first current.

\displaystyle I_2=2I_1

Use this equation to substitute current into the first equation.

\displaystyle I_1R_1=(2I_1)R_2

The initial current now cancels out from both sides.

\displaystyle R_1=2R_2

Divide both sides by two to isolate the final resistance variable.

\displaystyle \frac{1}{2}R_1=R_2

 

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