Question Video: Identifying the Direction of the Magnetic Field Created by a Current-Carrying Wire | Nagwa Question Video: Identifying the Direction of the Magnetic Field Created by a Current-Carrying Wire | Nagwa

# Question Video: Identifying the Direction of the Magnetic Field Created by a Current-Carrying Wire Physics • Third Year of Secondary School

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The diagram shows a cross section of a current-carrying wire. The magenta arrow shows the direction of the magnetic field at point ๐. Fill in the blank: The direction of the magnetic field at point ๐ is ๏ผฟ the direction of the field at point ๐.

03:25

### Video Transcript

The diagram below shows a cross section of a current-carrying wire. The magenta arrow shows the direction of the magnetic field at point ๐. Fill in the blank. The direction of the magnetic field at point ๐ is blank the direction of the field at point ๐. Weโve got three options to choose from. (A) At a right angle to, (B) opposite to, or (C) the same as.

So, in this question, weโre shown a diagram of a cross section of a wire, which is carrying a current, as well as two points labeled ๐ and ๐. We can also see a magenta, or pink, arrow here that shows us the direction of the magnetic field at point ๐. Weโre being asked to work out the direction of the magnetic field at point ๐.

Now, in order to figure this out, we can start by recalling that when a wire carries a current, a magnetic field is created around the wire. The magnetic field produced is always perpendicular to the direction of the current, which means that the magnetic field around a current-carrying wire will wrap around the wire, like this.

Now, the direction of this field can either be clockwise or counterclockwise. This depends on the direction of the current in the wire. Fortunately, thereโs an easy way to figure out the direction of the magnetic field if we know the direction of the current. And this is known as the right-hand rule. If we extend the thumb of our right hand and point it in the direction of a current, then our fingers will curl in the direction that the magnetic field is oriented.

Now, in this diagram, weโre looking at a cross section of a wire. This means that the current it carries must either be going into the screen or out of the screen. We can use the right-hand rule to see what happens in each case.

If the current were going into the page, which we can signify with a cross, then we can work out the direction of the magnetic field that would be created by pointing the thumb of our right hand into the screen. Doing this, we find that our fingers curl in a clockwise direction. This means that the magnetic field around the wire would go in a clockwise direction, too.

However, if we look carefully at the diagram, we can see that this conflicts with the information weโve been given. If the field went around the wire in a clockwise direction, then the magnetic field at point ๐ would point downward, not upward. This means that the current in the wire canโt be directed into the screen.

So how about if the current was directed out of the screen? We can represent this in our diagram by replacing our cross with a dot, like this. Applying the right-hand rule to this current, we point our right thumb out of the screen. Doing this, we find that this time our fingers curl counterclockwise. This means that the magnetic field around the wire will be oriented in a counterclockwise direction if the current is directed out of the screen. We can see that this fits with the fact that the magnetic field at point ๐ is pointing upward. So we know that in this scenario, the wire must be carrying a current out of the screen.

We can also see that because point ๐ is located to the right of the wire, the magnetic field at this point must also be pointing upward. And thatโs the same direction as at point ๐. So our final answer is option (C). The direction of the magnetic field at point ๐ must be the same as the direction of the magnetic field at point ๐.

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