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# Physics AS Level watch

1. Hey!

Im currently studying the CIE Physics AS Level Course.

Ive got one doubt in the Electric Fields Topic though!
For example,
Questeion: At a certain point in an electric field, the strength is 5 KN/C downwards.
Find the force on an electron placed at that point.

So we use the Formula E= F/Q

What I doubt in, is if we have to use the Positive value of Q (that is the elementary charge, 1.60x10^-19) or the negative one, since electrons are negative.

2. The direction of the electric field is by convention the direction of the force on a unit positive charge; so the force on an electron will be in the opposite direction.
3. Ah so if the Question said 5 KN/C upwards, then we would use the negative Charge?
4. If the question says the field is downwards, then
-the force on a positive charge is downwards
-the force on a negative change (like an electron) is upwards

The formula gives the magnitude of the force.

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