Nuclear

Question 1

What experiment proved the existence of a nucleus and how was it carried out

Answer 1

Rutherfords alpha scattering experiment

Firing a narrow beam of alpha particles all of the same KE at thin metal foil in an evacuated chamber

Question 2

Why was a narrow beam used

Answer 2

A narrow beam meant a small collision area which reduced the uncertainty in the scattering angle

Question 3

Why were the alpha particles all the same kinetic energy

Answer 3

Slower alpha particles would deflect more than fast alpha particles on the same initial path

Question 4

Why was a thin metal foil used

Answer 4

So it is thin enough for alpha particles to get through without being absorbed and sp scattering only occurred form one single metal nucleus

Question 5

Why was the experiment carried out in an evacuated chamber

Answer 5

Because alpha particles will only travel up to 5cm in air before being absorbed

Question 6

What did Rutherford expect would happen in the experiment

Answer 6

Alpha particles would undergo small deflections but otherwise travel more or less straight through the absorber due to their high density and speed

Question 7

What actually happened in the alpha scattering experiment

Answer 7

All alpha particles went straight through, but a small amount (1:8000) were back scattered or reflected by large angles

Question 8

What was Rutherfords explanation to what happened in the experiment (4 reasons)

Answer 8

-most of the atom was empty space because most alpha particles passed straight through the foil
-the nucleus must have a large positive charge , as some positively charged alpha particles were repelled and deflected by a large angle
-the nucleus must be very small as few particles were reflected back
-most of the mass is in the nucleus since the alpha particles (with high momentum) are deflected by the nucleus