AP Physics 1 : AP Physics 1

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #11 : Ohm's Law

If a closed circuit connected to a  battery has a resistance of , what is the current flowing through this circuit?

Possible Answers:

Correct answer:

Explanation:

This question can be solved by making use of Ohm's law, which states that the voltage difference across a circuit is proportional to the current flowing through the circuit, as well as to the resistance of the circuit. Written in equation form, we have:

Solving for current, we can rearrange to obtain:

Example Question #11 : Circuits

Determine the voltage drop across wire that is connected to two resistors in series with resistances  and , with a current flowing through the circuit of ?

Possible Answers:

Correct answer:

Explanation:

By Ohm's law:

, where  is the voltage drop across the wire.  is the current flowing through the wire, and  is the total resistance within the circuit. 

Since resistors are in series: 

, where  and  are the resistances of the two resistors. 

In our case:

Therefore:

Example Question #13 : Ohm's Law

A current of  passes through a circuit. A single resistor in this circuit has a resistance of . What is the voltage drop across this resistor?

Possible Answers:

Correct answer:

Explanation:

We need to use Ohm's law here which is given by:

Where  is the voltage in Volts,  is the current in Amperes, and  is the resistance in Ohms. We know the current in the circuit as well as the resistance of the resistor. We substitute our known values and solve for Voltage which will give us the voltage drop across the resistor.

 

Example Question #14 : Circuits

A circuit has a  power source and a  resistance.  What is the current in the circuit?

Possible Answers:

Correct answer:

Explanation:

We use Ohm's law, , to find the current in the circuit.  In Ohm's law  is the voltage in the circuit,  is the current in the circuit and  is the circuit's resistance.

Solving the equation for , we have

Example Question #14 : Ohm's Law

 battery has an internal resistance of .  If the current within the battery were to be measured using a multimeter, what magnitude would the meter record?

Possible Answers:

Correct answer:

Explanation:

We use Ohm's law, , to find the current in the circuit.  In Ohm's law  is the voltage in the circuit,  is the current in the circuit and  is the circuit's resistance.

Solving the equation for , we have

.

Example Question #16 : Circuits

What voltage is required to produce a  current in a circuit with a resistance?

Possible Answers:

Correct answer:

Explanation:

We use Ohm's law, , to find the current in the circuit.  In Ohm's law  is the voltage in the circuit,  is the current in the circuit and  is the circuit's resistance.

In our problem,

Example Question #17 : Circuits

If a circuit has a voltage of  and a current of , what is the resistance of the circuit?

Possible Answers:

Correct answer:

Explanation:

We use Ohm's law, , to find the current in the circuit.  In Ohm's law  is the voltage in the circuit,  is the current in the circuit and  is the circuit's resistance.

Solving Ohm's law for resistance gives us

.

Example Question #11 : Circuits

Emf

If the voltage drop across  is , what is the resistance or ?

Possible Answers:

Correct answer:

Explanation:

A few rules of circuits that will help here for series circuits are:

 

Method 1:

The current through  is given and that will be the same current going through  since there are no current junctions. Since the sum of all voltage drops must equal the emf of the battery, the voltage drop across  can be found:

We can use Ohm's law to find the resistance:

Method 2:

Ohm's law:

The resistance values are added to get , so

Solve for :

Example Question #11 : Ohm's Law

Which of the following statements is true?

Possible Answers:

None of these

Increasing the voltage will always increase the current flowing through a circuit and decreasing the resistance of a circuit will always decrease the current flowing through the circuit

Decreasing the resistance of a circuit will always decrease the current flowing through the circuit

Increasing the voltage will always increase the current flowing through a circuit

Correct answer:

None of these

Explanation:

To answer this question we need to use the definition of Ohm’s law.

where  is voltage,  is current, and  is resistance. As the equation suggests, to determine the effect of voltage on current we need information regarding the resistance. For example, increasing the voltage will increase the current if resistance decreases or if resistance stays the same. On the other hand, increasing the voltage will decrease the current if the resistance increases drastically; therefore, we cannot determine the effect of voltage on current without knowing anything about the resistance (we need to know if resistance increases, decreases, or stays the same). Similarly, we cannot determine the effect of resistance on the current without knowing about the voltage.

Example Question #17 : Ohm's Law

A student assembles a circuit with a resistor and a voltage source. He realizes that he needs to increase the amount of electrons flowing through the circuit to reach his goal. What can the student do to achieve this?

I. Change the voltage source to an alternating source

II. Use a new voltage source with higher voltage

III. Use another resistor with lower resistance

Possible Answers:

I and II

I and III

II and III

I, II and III

Correct answer:

II and III

Explanation:

Recall that the definition of current is the amount of electrons flowing through a circuit in a given amount of time. We can increase the amount of electrons flowing through a circuit (for a given time) if we increase the current. Using Ohm’s law, we can determine conditions that will increase the current.

Solving for current we get

This means we can get a high current if we increase voltage or decrease resistance. Note that that changing the voltage source from a direct source to an alternating source will generate an alternating current with similar amplitude; it won’t increase the total current of the system and, subsequently, the amount of electrons flowing through the circuit per given time.

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