Question Video: Determining the Direction of Current in a Wire | Nagwa Question Video: Determining the Direction of Current in a Wire | Nagwa

Question Video: Determining the Direction of Current in a Wire Science • Third Year of Preparatory School

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The picture shows the electrons and atomic nuclei in a section of copper wire. The blue circles represent electrons, and the red circles represent atomic nuclei. An electric potential difference is set up between the left-hand end and the right-hand end of the wire. This creates an electric current in it. Which of the arrows best shows the direction of the current in the wire?

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Video Transcript

The picture shows the electrons and atomic nuclei in a section of copper wire. The blue circles represent electrons, and the red circles represent atomic nuclei. An electric potential difference is set up between the left-hand end and the right-hand end of the wire. This creates an electric current in it. Which of the arrows best shows the direction of the current in the wire? (A) i, (B) ii, (C) iii, (D) iv.

First, let’s recall that an electric potential difference can exist between two points. Next, let’s recall that an electric potential difference between two points causes electric charges to flow from one of the points to the other. When electric charges flow together in the same direction, this is called an electric current. Electrons are electrically charged, and electrons can flow freely between atoms in an electrically conductive substance such as the copper that the wire in this question is made from.

We can say then that an electric potential difference across the length of a copper wire results in an electric current in the wire. The electrons that make up the current move between the sides of the wire which there is an electric potential difference across. The electrons all flow in the same direction. They do not change direction unless the direction of the electric potential difference across the wire is changed. Notice by the way that we’ve drawn the electrons moving in the opposite direction to the direction of the current, as conventional current is in the direction of positive charge flow, while electrons are negatively charged.

The question states that there is an electric potential difference between the left-hand side and the right-hand side of the wire. This means that the direction of the current must either be from left to right or from right to left. There is no way to tell from the question whether the direction is from left to right or from right to left. Whether the direction is from left to right or right to left, we can call the direction a horizontal direction, along this left-right axis. If we look at the options shown, we see that option (C), direction iii, shows the direction from left to right, which is a horizontal direction. The other options show directions that are either completely or partially vertical.

The correct answer is therefore option (C) iii.

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