AP Physics 2 : Electricity and Magnetism

Study concepts, example questions & explanations for AP Physics 2

varsity tutors app store varsity tutors android store

Example Questions

Example Question #231 : Electricity And Magnetism

A resistor has cross sectional area \(\displaystyle 2\textup{ mm}^2\) and length \(\displaystyle 1\textup{ cm}\). When placed in series with a \(\displaystyle 3\textup{ V}\) battery, a current of \(\displaystyle 340 \textup{ mA}\) is produced. Determine the resistivity.

Possible Answers:

\(\displaystyle 3.445*10^{-3}\ \Omega\cdot \textup{m}\)

\(\displaystyle 9.996*10^{-3}\ \Omega\cdot \textup{m}\)

None of these

\(\displaystyle 1.764*10^{-3}\ \Omega\cdot \textup{m}\)

\(\displaystyle 8.221*10^{-3}\ \Omega\cdot \textup{m}\)

Correct answer:

\(\displaystyle 1.764*10^{-3}\ \Omega\cdot \textup{m}\)

Explanation:

Using Ohm's law:

\(\displaystyle V=IR\)

Converting \(\displaystyle mA\) to \(\displaystyle A\) and plugging in values

\(\displaystyle 3=.340*R\)

Solving for resistance:

\(\displaystyle R=8.82\Omega\)

Using the equation for resistivity:

\(\displaystyle \rho=R\frac{A}{l}\)

Converting \(\displaystyle mm^2\) to \(\displaystyle m\) and \(\displaystyle cm\) to \(\displaystyle m\) and plugging in values:

\(\displaystyle \rho=8.82\frac{2*10^{-6}}{.01}\)

\(\displaystyle \rho=1.764*10^{-3}\Omega\cdot m\)

Example Question #64 : Circuit Properties

A resistor has cross sectional area \(\displaystyle 16\textup{ mm}^2\) and length \(\displaystyle 2\textup{ cm}\). When placed in series with a \(\displaystyle 3\textup{ V}\) battery, a current of \(\displaystyle 56.0\textup{ mA}\) is produced. Determine the resistivity.

Possible Answers:

None of the above

\(\displaystyle \rho=1.213*10^{-3}\ \Omega\cdot \textup{m}\)

\(\displaystyle \rho=3.751*10^{-3}\ \Omega\cdot \textup{m}\)

\(\displaystyle \rho=1.764*10^{-3}\ \Omega\cdot \textup{m}\)

\(\displaystyle \rho=2.028*10^{-3}\ \Omega\cdot \textup{m}\)

Correct answer:

\(\displaystyle \rho=1.764*10^{-3}\ \Omega\cdot \textup{m}\)

Explanation:

Using Ohm's law:

\(\displaystyle V=IR\)

Converting \(\displaystyle mA\) to \(\displaystyle A\) and plugging in values

\(\displaystyle 3=.340*R\)

Solving for resistance:

\(\displaystyle R=8.82\Omega\)

Using the equation for resistivity:

\(\displaystyle \rho=R\frac{A}{l}\)

Converting \(\displaystyle mm^2\) to \(\displaystyle m\) and \(\displaystyle cm\) to \(\displaystyle m\) and plugging in values:

\(\displaystyle \rho=8.82\frac{2*10^{-6}}{.01}\)

\(\displaystyle \rho=1.764*10^{-3}\Omega*m\)

Example Question #61 : Circuit Properties

A resistor is made out of a material. The resistor has a cross-sectional area of \(\displaystyle 4mm^2\) and a length of \(\displaystyle 8mm\). It is found to have a resistance of \(\displaystyle 7\Omega\). A new resistor is built that has a length of \(\displaystyle 6mm\) and a cross sectional area of \(\displaystyle 3.3mm^2\). Determine the resistance of the new resistor.

Possible Answers:

\(\displaystyle 6.36\Omega\)

\(\displaystyle 3.95\Omega\)

\(\displaystyle 4.05\Omega\)

None of these

\(\displaystyle 7.77\Omega\)

Correct answer:

\(\displaystyle 6.36\Omega\)

Explanation:

Using

\(\displaystyle \rho=R\frac{A}{l}\)

Plugging in values

\(\displaystyle \rho=7*\frac{4}{8}\)

\(\displaystyle \rho=3.5\Omega*mm\)

Using 

\(\displaystyle R=\rho*\frac{l}{A}\)

Plugging in values

\(\displaystyle R=3.5*\frac{6}{3.3}\)

\(\displaystyle R=6.36\Omega\)

Example Question #66 : Circuit Properties

\(\displaystyle 3\) identical resistors are placed in parallel. They are placed in a circuit with a \(\displaystyle 4V\) battery. If the current through the battery is \(\displaystyle 3A\), determine the resistivity of each resistor. Each resistor is \(\displaystyle 3cm\) long and has a diameter of \(\displaystyle 1cm\).

Possible Answers:

\(\displaystyle \rho_1=\rho_2=\rho_3=.79\Omega\cdot cm\)

\(\displaystyle \rho_1=.79\Omega\cdot cm\)

\(\displaystyle \rho_2=\rho_3=1.50\Omega\cdot cm\)

\(\displaystyle \rho_1=\rho_2=\rho_3=2.27\Omega\cdot cm\)

None of these

\(\displaystyle \rho_1=\rho_2=\rho_3=1.50\Omega\cdot cm\)

Correct answer:

\(\displaystyle \rho_1=\rho_2=\rho_3=.79\Omega\cdot cm\)

Explanation:

Since each resistor is in parallel, the voltage drop across each will be \(\displaystyle 4V\).

Since each resistor is identical, they all have the same resistance.

Using

\(\displaystyle I_1+I_2+I_3=I_{total}=3A\)

and

\(\displaystyle I_1=I_2=I_3\)

It is determined that

\(\displaystyle I_1=I_2=I_3=1A\)

Using

\(\displaystyle V=IR\)

\(\displaystyle 3=1*R\)

\(\displaystyle R=3\Omega\) for all three resistors

Using definition of resistivity:

\(\displaystyle \rho=R\frac{A}{l}\)

\(\displaystyle \rho=3*\frac{\pi*.5^2}{3}\)

\(\displaystyle \rho=.79\Omega\cdot cm\)

Example Question #231 : Electricity And Magnetism

A resistor is made out of a material. The resistor has a cross-sectional area of \(\displaystyle 2mm^2\) and a length of \(\displaystyle 3mm\). It is found to have a resistance of \(\displaystyle 6\Omega\). Determine the resistivity of the material.

Possible Answers:

\(\displaystyle 4\Omega\cdot mm\)

\(\displaystyle 2\Omega\cdot mm\)

\(\displaystyle 4\Omega\cdot mm\)

\(\displaystyle 6\Omega\cdot mm\)

None of these

Correct answer:

\(\displaystyle 4\Omega\cdot mm\)

Explanation:

Use the equation for resistivity:

\(\displaystyle \rho=R\frac{A}{l}\)

Plugging in values

\(\displaystyle \rho=6*\frac{2}{3}\)

\(\displaystyle \rho=4\Omega\cdot mm\)

Example Question #231 : Electricity And Magnetism

A resistor is made out of a material. The resistor has a cross-sectional area of \(\displaystyle 2mm^2\) and a length of \(\displaystyle 3mm\). It is found to have a resistance of \(\displaystyle 6\Omega\). A new resistor is built that has a length of \(\displaystyle 4mm\) and a cross sectional area of \(\displaystyle 1.5mm^2\). Determine the resistance of the new resistor.

Possible Answers:

\(\displaystyle 10.7\Omega\)

\(\displaystyle 6.37\Omega\)

\(\displaystyle 4.17\Omega\)

\(\displaystyle 4\Omega\)

None of these

Correct answer:

\(\displaystyle 10.7\Omega\)

Explanation:

Use the equation for resistivity:

\(\displaystyle \rho=R\frac{A}{l}\)

Plugging in values

\(\displaystyle \rho=6*\frac{2}{3}\)

\(\displaystyle \rho=4\Omega\cdot mm\)

Using 

\(\displaystyle R=\rho*\frac{l}{A}\)

Plugging in values

\(\displaystyle R=4*\frac{4}{1.5}\)

\(\displaystyle R=10.7\Omega\)

Example Question #881 : Ap Physics 2

A resistor is made out of a material. The resistor has a cross-sectional area of \(\displaystyle 2mm^2\) and a length of \(\displaystyle 3mm\). It is found to have a resistance of \(\displaystyle 6\Omega\). A new resistor is built that has a length of \(\displaystyle 4mm\) and a cross sectional area of \(\displaystyle 1.5mm^2\). The new resistor is placed in series with a \(\displaystyle 6V\) battery. Determine the current through the resistor.

Possible Answers:

\(\displaystyle .11A\)

\(\displaystyle .23A\)

\(\displaystyle .89A\)

\(\displaystyle .56A\)

None of these

Correct answer:

\(\displaystyle .56A\)

Explanation:

Use the equation for resistivity:

\(\displaystyle \rho=R\frac{A}{l}\)

Plugging in values

\(\displaystyle \rho=6*\frac{2}{3}\)

\(\displaystyle \rho=4\Omega\cdot mm\)

Rearrange the same equation and solve for resistance:

\(\displaystyle R=\rho*\frac{l}{A}\)

Plugging in values

\(\displaystyle R=4*\frac{4}{1.5}\)

\(\displaystyle R=10.7\Omega\)

Use Ohm's law to find current:

\(\displaystyle V=IR\)

\(\displaystyle 6=I*10.7\)

\(\displaystyle I=.56A\)

Example Question #71 : Circuits

A scientist is testing resistors made of the same material. Resistor \(\displaystyle A\) has a cross sectional area of \(\displaystyle 3mm^2\) and a length of \(\displaystyle 3mm^2\). Resistor \(\displaystyle B\) has a cross sectional area of \(\displaystyle 6mm^2\) and a length of \(\displaystyle 3mm^2\). How will the resistance of \(\displaystyle B\) compare to that of \(\displaystyle A\)?

Possible Answers:

The resistance will quadruple

None of these

The resistance will double

The resistance will be cut in half

The resistance will stay the same

Correct answer:

The resistance will be cut in half

Explanation:

Use the equation for resistivity to visualize the proportions:

\(\displaystyle R=\rho*\frac{l}{A}\)

\(\displaystyle \rho\) will stay constant as the material is the same. \(\displaystyle A\) doubles and \(\displaystyle l\) stays the same. Thus, the resistance, \(\displaystyle R\), will get cut in half.

Example Question #71 : Circuit Properties

A resistor is made out of a material. The resistor has a cross-sectional area of \(\displaystyle 4mm^2\) and a length of \(\displaystyle 8mm\). It is found to have a resistance of \(\displaystyle 7\Omega\). Determine the resistivity of the material.

Possible Answers:

\(\displaystyle 4.7\Omega\cdot mm\)

\(\displaystyle 6.5\Omega\cdot mm\)

\(\displaystyle 7.0\Omega\cdot mm\)

\(\displaystyle 10.3\Omega\cdot mm\)

\(\displaystyle 3.5\Omega\cdot mm\)

Correct answer:

\(\displaystyle 3.5\Omega\cdot mm\)

Explanation:

Using

\(\displaystyle \rho=R\frac{A}{l}\)

Plugging in values

\(\displaystyle \rho=7*\frac{4}{8}\)

\(\displaystyle \rho=3.5\Omega\cdot mm\)

Example Question #71 : Circuits

A resistor is made out of a material. The resistor has a cross-sectional area of \(\displaystyle 4mm^2\) and a length of \(\displaystyle 8mm\). It is found to have a resistance of \(\displaystyle 7\Omega\). A new resistor is built that has a length of \(\displaystyle 6mm\) and a cross sectional area of \(\displaystyle 3.3mm^2\). The new resistor is placed in series with a \(\displaystyle 6V\) battery. Determine the current through the resistor.

Possible Answers:

\(\displaystyle .94A\)

None of these

\(\displaystyle 3.25A\)

\(\displaystyle 1.94A\)

\(\displaystyle 1.25A\)

Correct answer:

\(\displaystyle .94A\)

Explanation:

Using

\(\displaystyle \rho=R\frac{A}{l}\)

Plugging in values

\(\displaystyle \rho=7*\frac{4}{8}\)

\(\displaystyle \rho=3.5\Omega*mm\)

Using 

\(\displaystyle R=\rho*\frac{l}{A}\)

Plugging in values

\(\displaystyle R=3.5*\frac{6}{3.3}\)

\(\displaystyle R=6.36\Omega\)

Using

\(\displaystyle V=IR\)

Solving for \(\displaystyle I\)

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

\(\displaystyle I=\frac{6}{6.36}\)

\(\displaystyle I=.94A\)

Learning Tools by Varsity Tutors