Question Video: Identifying a Vector Quantity Physics • 9th Grade

Which of the following is a vector quantity? [A] Energy [B] Pressure [C] Potential difference [D] Force [E] Charge


Video Transcript

Which of the following is a vector quantity? (A) Energy, (B) pressure, (C) potential difference, (D) force, (E) charge.

Okay, so the idea here is that one of these five quantities is a vector. And we can recall that a vector quantity is defined as having both magnitude as well as direction. And specifically, it’s the fact that a vector has a direction associated with it that sets it apart from what’s called a scalar quantity, which is a quantity that only has magnitude. So, as we look over our different answer options, let’s consider examples of each one of these quantities and see if we find any directions along with magnitudes.

Starting out with choice (A), energy, an example amount of energy might be this: 12 joules. When it comes to pressures, the standard unit for reporting a pressure in is the pascal. The standard unit for reporting a potential difference is the volt. We might have, say, 32 volts. While the SI based unit of force is the newton, we might have a force say of 13 newtons to the right. And amounts of charge are typically reported in units of coulombs. We could have 0.3 coulombs of charge.

In all of these example quantities, we see that there are magnitudes: 12 joules, 3.1 pascals, 32 volts, and so on. But by our definition of what a vector quantity is, magnitude alone is not enough to create a vector. We also need a direction associated with that magnitude. Requiring this to be true, we see that only one of our five options has a direction. That’s the force, which is a force of 13 newtons to the right. Here then we have a magnitude, 13 newtons, and a direction. And none of the other quantities have a direction. So we’ll choose answer option (D), force, as the only vector quantity listed here.

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