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Chapter 17 - Electric Fields
Terms in this set (19)
Equation for Force (N) in an Electric Field
Equation for Potential Energy (J) in an Electric Field
Equation for Field Strength (V/m) of an Electric Field
Equation for Potential (Voltage, V) in an Electric Field
What do parallel plates mean for an Electric Field?
The field is uniform
In a uniform field, how are the equipotentials spaced?
Which direction do the +ve ions travel in an electric field?
From the +ve plate to the -ve plate
From E=F/Q and E=V/d, which can be used in all fields and which can only be used in uniform fields?
E=F/Q - All Fields. E=V/d - Uniform Fields only
In Millikans oil drop experiment, what caused the oil drop to be stationary/travel in a straight line?
The Electric Field Strength upwards matched the weight of the oil drop downwards
What happens to the radius of an ion's path in an electric field if it's mass increases? Why is this?
Bigger mass means a bigger radius. r=mv/Bq, so if m is larger and all others remain constant, then r will also become larger.
mv^2/r = Bqv.
Non-uniform fields - Describe the "spike" plate arrangement.
One of the plates has a spike, and the strongest field is at the tip of the spike. The equipotentials are curved around the tip of the spike.
Non-uniform fields - Describe the "point charge" and flat plate arrangement.
A single point contains a charge with a plate below it, and the equipotentials are curved around the charge and become more spaced out as they get closer to the plate.
Non-uniform fields - Describe the "point charge" circular plate arrangement.
There is a charge in the middle of a circular plate, and the equpiotentials space out as you move away from the centre of the circular plate.
If a ball is bouncing between two plates, being charged +vely and -vely as it bounces, how can a reading on an ammeter attached to the circuit be increased and why does it increase?
Increase EMF, or make a smaller gap between the plates. This increases the reading because it increases the speed of the ball bouncing between the two plates, carrying more charge across the plates.
What does 1 electron volt (eV) represent?
The energy gained (J) by an electron when accelerated through one Volt of Potential Difference.
How was Millikan's oil-drop experiment used to find the charge of an electron?
F = qE, E=V/d, so qV/d = mg.
Therefore q = (mgd)/V.
They found values of -1.6x10⁻¹⁹ (or multiples of this), but not lower. They concluded this was the charge of an electron.
Why do electrons take a curved path in an electron gun?
Once they have "boiled off" the hot cathode and are accelerated, there are no horizontal forces acting on them.
There is only the vertical forces of electrical attraction between the +ve top plate and -ve electrons. This means they are deflected upwards.
The path they take is a parabola.
How is the speed of a particle (usually electron) calculated?
Equate F = mv²/r and F = Bev,
mv²/r = Bev,
mv/r = Be,
So v = (Ber)/m.
Out of the 4 electric field equations, which are vectors and which are scalars?
E(field strength) and F(electric) are vector.
V and E are scalar.
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