# Question Video: Understanding Diodes Physics • 9th Grade

Which of the following correctly describes a diode? [A] A diode is an electronic component that emits light with a very high efficiency. [B] A diode is an electronic component with a resistance that changes depending on how much light is incident upon it. [C] A diode is an electronic component that only allows a current to flow in one direction through it. [D] A diode is an electronic component that can be used to amplify signals. [E] A diode is an electronic component with a resistance that changes depending on ambient temperature.

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### Video Transcript

Which of the following correctly describes a diode? A) A diode is an electronic component that emits light with a very high efficiency. B) A diode is an electronic component with a resistance that changes depending on how much light is incident upon it. C) A diode is an electronic component that only allows a current to flow in one direction through it. D) A diode is an electronic component that can be used to amplify signals. E) A diode is an electronic component with a resistance that changes depending on ambient temperature.

Okay, so in this question, out of the options A to E, we’ve been asked to select the one that describes a diode. To answer this, it might help to remember the circuit symbol of a diode. This is how we draw a diode in a circuit diagram. And this diagram is particularly helpful to us because, in this diagram, we can see that there’s a little arrow. And we can recall that this arrow signifies the direction in which conventional current is allowed to flow through a diode. In other words, conventional current, that’s current made up of positive charges, can flow in that direction but is not allowed to flow in the other direction. And that is the functionality of a diode. In other words then, a diode is an electronic component that only allows a current to flow in one direction through it. Hence, that is the answer to our question.

Very quickly looking at the other options though, we can see that the description in option A is that a diode is an electronic component that emits light with a very high efficiency. Well, that type of component is actually a very specific kind of diode, specifically, a light emitting diode or LED. And LEDs do actually emit light with very high efficiency. However, this is not a good description of a diode in general because not all diodes are light emitting diodes. And, hence, we haven’t picked option A as the answer to our question.

Option B says that a diode is an electronic component with a resistance that changes depending on how much light is incident upon it. Well, that sounds more like a description of a light-dependent resistor or an LDR. And so, that’s not the answer to our question either. Option D says that a diode is an electronic component that can be used to amplify signals. Well, that sounds very much like an amplifier, which are often made up of transistors as well as others circuit components of course. And so, this does not sound like a description of a diode. And, finally, option E says that a diode is an electronic component with a resistance that changes depending on ambient temperature. Well, that circuit component is known as a thermistor, or sometimes a temperature-dependent resistor. And, hence, option E is also not the answer to our question.