17.1

Question 1

What does CERN’s hadron collider do?

Answer 1

CERN’s hadron collider uses a voltage to accelerate charged particles.

Question 2

What happens when a proton crosses an electrical field?

Answer 2

When a particle of positive charge moves to the negative terminal it gains KE and loses electrical potential energy.

Question 3

What’s the formula for work done?

Answer 3

For uniform fields, force is constant. Work done on the field is force * distance. Electrical force = electric field * charge, so work done = qEd=Vq

Question 4

What’s the electric field formula?

Answer 4

E=V/d

Question 5

What are equipotentials and what’s the formula for electric fields when the line curves?

Answer 5

Equipotential surfaces link points of equal potential and form equally spaced planes. When the lines curve, E=-dV/dr. E field is in opposite direction to increasing V.
At 1/2 V the E field is weakest, 0.58Vd^-1.

Question 6

What defines an electric field?

Answer 6

Force per unit positive charge

Question 7

How is Milikan’s oil drop experiment carried out?

Answer 7

In 1897 JJ Thomson knew the charge-mass ratio of an electron but the charge was unknown. Robert Milikan found the charge.
Oil is squirted through a hole in a metal plate and falls as tiny droplets which are ionised by a weak radioactive source. Applying a PD across the plates creates an electric field, when the electric and gravitational fields are equal the droplet is suspended. The drop reaches terminal velocity when the PD is switched off. The fall is timed, and air viscosity used to calculate the radius of the drop. As density is known, the mass of the drop is then found. Charge is found using q=mgd/V.