All AP Physics 2 Resources
Example Questions
Example Question #71 : Circuits
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 ?
The resistance will quadruple
None of these
The resistance will double
The resistance will be cut in half
The resistance will stay the same
The resistance will be cut in half
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 #71 : Circuit Properties
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.
Using
Plugging in values
Example Question #71 : Circuits
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.
None of these
Using
Plugging in values
Using
Plugging in values
Using
Solving for
Example Question #74 : Circuit Properties
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 ?
It is impossible to determine
None of these
The resistance of will be a quarter of that of
They will be the same
The resistance of will be a quarter of that of
The resistance of will be a quarter of that of
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 #881 : Ap Physics 2
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.
None of these
Determining the resistance
Using
Example Question #71 : Circuits
A scientist carves out a cylinder of a new material she developed. It is tall, with a radius of . She puts electrodes on each face of the cylinder. She determines the resistance to be . What is the resistivity of this new material?
None of these
Using the relationship:
Here, is the resistivity, is the resistance, is cross sectional area, and is the length.
The area of a circle is:
Substitute:
Plug in given values and solve.
Example Question #1 : Circuit Power
Consider the circuit:
What is the rate of power consumption in the circuit if every resistor has a resistance of ?
To calculate the power consumption of the circuit, we need to first reduce it to an equivalent circuit with a single resistor. Since each resistor has the same resistance, this solution will keep resistance calculations as multiples of until the circuit is fully reduced.
Start with the two branches in parallel. We can condense R3 and R4, then solve for the total resistance of R2, R3, and R4.
The equivalent circuit now has three resistors in series (R1, Req, and R5), so we can simply add them all up:
Plug in the value for R:
Now we can use the equation for power:
Substituting in Ohm's law for current, we get:
Example Question #2 : Circuit Power
You have 4 resistors, , , , and , set up like this:
Their resistance are as follows:
If the battery has 8V, what is the total power dissipated through the resistors?
The equation for power is
In order to get the power, we need the current. To find the current, we need to get the total resistance, and use Ohm's Law ().
To find the total resistance, remember the equations for adding resistors is this:
Resistors and are in series, resistors and are in parallel, and resistors and are in series.
Now, we can find the current.
Finally, we can find the power.
Therefore, the power is 16W (watts).
Example Question #2 : Circuit Power
Calculate the power consumed across resistor .
To calculate power, we need two of the following three quantities: voltage, current, and resistance.
In this case, since we are lacking the voltage, let's try to find the current.
We can use Kirchoff's junction law to calculate current .
The current coming into the junction = the current coming out of the junction.
Let's take a look at the central junction to the right of resistor .
Now that we know and , we can calculate power across the resistor.
Example Question #1 : Circuit Power
Elements A-D represent light bulbs.
Which of the following is true about these two circuits? Assume voltage sources have the same value and all the light bulbs are all identical.
Bulbs C and D have different brightnesses.
All bulbs will have the same brightness.
Bulbs A and B will be brighter than bulbs C and D.
Bulbs A and B have different brightnesses.
Bulb A will be as bright as bulb C, but bulbs B and D will have a different brightness.
Bulbs A and B will be brighter than bulbs C and D.
Since bulbs A and B are in parallel, they will have the same voltage, and since the bulbs are identical in resistance, they will have the same current running through them and will be just as bright.
Let's say the voltage source as a value of and each bulb has a resistance of .
The current going through bulbs A and B is .
However, the current going through bulbs C and D is .
The current going through bulbs C and D is half as much as the other two, so their brightness will be less.
So, bulbs A and B will be brigher than bulbs C and D.