All AP Physics 1 Resources
Example Questions
Example Question #212 : Electricity And Waves
Which of the following wires with a current running through them would have the least resistance?
They would all have equal resistance
Wire B: and
Wire C: and
Wire D: and
Wire A: and
Wire B: and
The correct answer is Wire B with and of current.
The formula for voltage, current and resistance is as follows:
Thus, the wire with the lowest ratio of voltage to current will have the least resistance.
Example Question #11 : Current And Voltage
What is the current in the given circuit if , and ?
To find the current we must first find the equivalent resistance. For resistors in series, the equivalent resistance is
For this problem
Now we use Ohm's law, , to find the current,
Example Question #1363 : Ap Physics 1
What is the current in the given circuit if , and ?
To find the current we must first find the equivalent resistance. For resistors in parallel, the equivalent resistance is
For this problem
Now we use Ohm's law, , to find the current,
Example Question #21 : Current And Voltage
What is the current in the given circuit if , , and ?
To find the current we must first find the equivalent resistance. This problem is a combination of resistors in series and parallel. First we find the equivalent resistance of resistors in series.
For resistors in series, the equivalent resistance is:
For this problem
The resistors in series can be treated as one resistor. Now we address the resistors in parallel. For resistors in parallel, the equivalent resistance is:
For this problem
Now we use Ohm's law, , to find the current,
Example Question #1 : Resistivity
Consider the circuit:
The current flowing through the entire circuit is . What is the value of R3?
We know the voltage and total current of the circuit, so we can calculate an equivalent resistance using Ohm's law:
Now we can use the expression for condensing parallel resistors to calculate R3:
Example Question #1 : Resistivity
Which of the following factors would decrease the resistance through an electrical cord?
Increasing the resistivity
Increasing the length of the cord
Decreasing the cross-sectional area of the cord
Increasing the cross-sectional area of the cord
Increasing the cross-sectional area of the cord
The equation for resistance is given by .
From this equation, we can see the best way to decrease resistance is by increasing the cross-sectional area, , of the cord. Increasing the length, , of the cord or the resistivity, , will increase the resistance.
Example Question #3 : Resistivity
An electrician wishes to cut a copper wire that has no more than of resistance. The wire has a radius of 0.725mm. Approximately what length of wire has a resistance equal to the maximum ?
2.6cm
960m
38m
9.6m
10cm
960m
To relate resistance R, resistivity , area A, and length L we use the equation.
Rearranging to isolate the quantity we wish to solve for, L, gives the equation . We must first solve for A using the radius, 0.725mm.
Plugging in our numbers gives the answer, 960m.
Example Question #141 : Electricity
What is the current in a circuit with a resistor followed by a resistor that are both in parallel with a resistor? The voltage supplied to the circuit is 5V.
Resistors in serries add according to the formula:
Resistors in parallel add according to the formula:
We can find the total equivalent resistance:
Now we can use Ohm's law to find the current:
Solve:
Example Question #2 : Resistivity
In the circuit above, your aim is to limit the current to , so you must design a resistor to serve in the place of .
To make this resistor, you have a spool of mystery metal, which has a cross sectional area of and a resistivity of, . What length of wire should you cut?
First, find out how much total resistance should be in the circuit in order to get the desired current:
Determine what the second resistance should be.
Find the necessary length of wire.
Example Question #1 : Resistivity
What is the resistance of a length of round copper wire with a radius of ?
Resistance and resistivity are related as follows: