AP Physics 2 : Resistivity

Study concepts, example questions & explanations for AP Physics 2

varsity tutors app store varsity tutors android store

Example Questions

Example Question #21 : Resistivity

A resistor is made out of a material. The resistor has a cross-sectional area of  and a length of . It is found to have a resistance of . A new resistor is built that has a length of  and a cross sectional area of . Determine the resistance of the new resistor.

Possible Answers:

None of these

Correct answer:

Explanation:

Using

Plugging in values

Using 

Plugging in values

Example Question #22 : Resistivity

 identical resistors are placed in parallel. They are placed in a circuit with a  battery. If the current through the battery is , determine the resistivity of each resistor. Each resistor is  long and has a diameter of .

Possible Answers:

None of these

Correct answer:

Explanation:

Since each resistor is in parallel, the voltage drop across each will be .

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

Using

and

It is determined that

Using

 for all three resistors

Using definition of resistivity:

Example Question #23 : Resistivity

A resistor is made out of a material. The resistor has a cross-sectional area of and a length of . It is found to have a resistance of . Determine the resistivity of the material.

Possible Answers:

None of these

Correct answer:

Explanation:

Use the equation for resistivity:

Plugging in values

Example Question #24 : Resistivity

A resistor is made out of a material. The resistor has a cross-sectional area of and a length of . It is found to have a resistance of . A new resistor is built that has a length of and a cross sectional area of . Determine the resistance of the new resistor.

Possible Answers:

None of these

Correct answer:

Explanation:

Use the equation for resistivity:

Plugging in values

Using 

Plugging in values

Example Question #25 : Resistivity

A resistor is made out of a material. The resistor has a cross-sectional area of and a length of . It is found to have a resistance of . A new resistor is built that has a length of and a cross sectional area of . The new resistor is placed in series with a battery. Determine the current through the resistor.

Possible Answers:

None of these

Correct answer:

Explanation:

Use the equation for resistivity:

Plugging in values

Rearrange the same equation and solve for resistance:

Plugging in values

Use Ohm's law to find current:

Example Question #26 : Resistivity

A scientist is testing resistors made of the same material. Resistor has a cross sectional area of and a length of . Resistor has a cross sectional area of  and a length of . How will the resistance of compare to that of ?

Possible Answers:

The resistance will quadruple

The resistance will stay the same

The resistance will be cut in half

None of these

The resistance will double

Correct answer:

The resistance will be cut in half

Explanation:

Use the equation for resistivity to visualize the proportions:

 will stay constant as the material is the same.  doubles and  stays the same. Thus, the resistance, , will get cut in half.

Example Question #21 : Resistivity

A resistor is made out of a material. The resistor has a cross-sectional area of  and a length of . It is found to have a resistance of . Determine the resistivity of the material.

Possible Answers:

Correct answer:

Explanation:

Using

Plugging in values

Example Question #28 : Resistivity

A resistor is made out of a material. The resistor has a cross-sectional area of  and a length of . It is found to have a resistance of . A new resistor is built that has a length of  and a cross sectional area of . The new resistor is placed in series with a  battery. Determine the current through the resistor.

Possible Answers:

None of these

Correct answer:

Explanation:

Using

Plugging in values

Using 

Plugging in values

Using

Solving for 

Example Question #29 : Resistivity

A scientist is testing resistors made of the same material. Resistor  has a cross sectional area of  and a length of . Resistor  has a cross sectional area of  and a length of . How will the resistance of  compare to that of ?

Possible Answers:

It is impossible to determine

The resistance of  will be a quarter of that of 

None of these

They will be the same

The resistance of  will be a quarter of that of 

Correct answer:

The resistance of  will be a quarter of that of 

Explanation:

Using

 will stay constant as the material is the same.  increases by a ratio of , and  decreases by a ratio of  . Thus, the resistance, , will decrease to a quarter of it's original value. 

Example Question #30 : Resistivity

A cubic resistor is placed in a circuit. If each edge measures  long, the voltage of the battery is  and the current through the resistor is , determine the resistivity.

Possible Answers:

None of these

Correct answer:

Explanation:

Determining the resistance

Using

Learning Tools by Varsity Tutors