# AP Physics 2 : Right Hand Rule for Current-Carrying Wire

## Example Questions

### Example Question #1 : Right Hand Rule For Current Carrying Wire

Consider the given wire:

In which direction should the electrons flow through the wire if the electric field generated inside the loop points out of the screen?

None of these

Into the screen

Clockwise

Counterclockwise

Out of the screen

Clockwise

Explanation:

We need to use the right hand rule to solve this problem. However, the right hand rule applies to the flow of current, which is in the opposite direction of the actual flow of electrons (current is defined, in this case, as the direction of proton flow). Therefore, you can either use the right hand rule and reverse what you determine, or simply use your left hand.

Let's just use our left hand. Point your thumb out and curl your fingers. Your fingers should be pointing at you. This is the direction of the electric field when electrons are traveling the direction of your thumb. If you lay your left thumb along the wire loop on the left side of the loop, our fingers are inside the loop and pointing out of the screen. This is the scenario we are looking for. Therefore, the electrons need to flow clockwise around the loop.

Note that the electrons must flow through the wire, eliminating the answer options for "into the screen" and "out of the screen."

### Example Question #1 : Right Hand Rule For Current Carrying Wire

You have two current-carrying wires layed parallel to each other like below.

Point R is halfway between each of the wires. If the wires carry the same current I, what is the direction of the magnetic field at point R?

Into the screen

There is no magnetic field at point .

Left

Out of the screen

Right

There is no magnetic field at point .

Explanation:

Using the right hand rule, we can tell that the direction of the magnetic field due to the bottom wire is out of the screen. Likewise, we can tell that the magnetic field due to the top wire is into the screen. Because point R is halfway between the two wires, they each have the same strength. Therefore, they both cancel each other out, leaving no magnetic field.

### Example Question #3 : Right Hand Rule For Current Carrying Wire

In the figure above, there are two wires carrying different currents in the same direction.

What is the direction of the magnetic field at point ?

Upwards

Downwards

Into the screen

Out of the screen

To the right

Out of the screen

Explanation:

Let's use the right-hand rule to determine the magnetic field cause by each current.

For current , we determine that the magnetic field is going into the screen.

For current , we determine that the magnetic field is going out of the screen.

Do the two directions cancel out? Well, the magnitude of  is greater than the magnitude of , meaning that  will overpower , so the net direction is out of the screen.

### Example Question #2 : Right Hand Rule For Current Carrying Wire

In the given diagram, what is the direction of the magnetic field at a point ?

Out of the screen

To the right

Into the screen

Towards the bottom of the screen

To the left

Out of the screen

Explanation:

Recall that the convention for the direction of current is from the positive end of the voltage source to the negative end (opposite the direction of flow of electrons). Thus, in this circuit the current is flowing counterclockwise from the voltage source. Using the right hand rule for the conventional current in the wire, the right thumb is pointed along the wire pointing to the left. At point the fingers curl around and point up, out of the screen. This can be verified by putting the thumb in the direction of current anywhere in the circuit. For example, if we take the direction of the current across the resistor, our thumb points down. Curling our fingers around the wire, the fingers will again point out of the screen at point , verifying our initial answer.

### Example Question #4 : Right Hand Rule For Current Carrying Wire

In the given diagram, what is the direction of the magnetic field at a point ?

Towards the top of the screen

Into the screen

Towards the bottom of the screen

Out of the screen

To the left

Into the screen

Explanation:

Current flows counterclockwise in this circuit. Using the right hand rule for the conventional current in the wire, the right thumb is pointed along the wire pointing to the left at the top of the circuit. At point the fingers curl around and point down, into the screen.

### Example Question #3 : Right Hand Rule For Current Carrying Wire

What is the direction of the magnetic field at a point ?

Out of the screen

To the right

Into the screen

Up towards the top of the screen

To the left

Into the screen

Explanation:

The current flows through this circuit counterclockwise. Using the right hand rule for the conventional current in the wire, the right thumb is pointed along the wire pointing to the right in the wire at the bottom of the circuit. At point the fingers curl around and point down, into the screen.

### Example Question #4 : Right Hand Rule For Current Carrying Wire

The magnetic field of the earth points from geographic south to geographic north, indicating the the geographic south pole is actually a magnetic south pole. If this magnetic south pole were generated by current around the equator moving in a wire, which way would the conventional current be traveling?

North to south

West to east

None of these

East to west

South to north