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Example Questions
Example Question #1 : Resistivity
Which of the following factors would decrease the resistance through an electrical cord?
Increasing the cross-sectional area of the cord
Decreasing the cross-sectional area of the cord
Increasing the length of the cord
Increasing the resistivity
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 #111 : Circuits
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
?
960m
10cm
9.6m
38m
2.6cm
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 #61 : Circuits
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:
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All MCAT Physical Resources
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