AS Physics Chapter 3.2 Summary Questions

Hey,
I got a bit stuck on one of the questions on chapter 3.2 of the Physics AS book.
Usually when i'm stuck on a question I just look at the answer, but as the question requires a written answer, it doesn't have one =/
It's Questions 1a and 1b...

Q1) A Vacumm photocell is connected to a microammeter. Explain the following observations.
a) When the cathode was illuminated with blue light of low intensity, the microammeter showed a non-zero reading

b) When the cathode was illuminated with an intense red light, the microammeter reading was zero.

please help :frown:

Reply 1

Stonebridge

13

The photocell uses photoelectric emission of electrons to give the current.
Have you done the photoelectric effect?
If so, then you will know the effect (on the emission of the electrons) of increasing the wavelength or the intensity of the light you shine on the surface.

Reply 2

Aleprechaun

3

A. The blue light has a higher frequency then the threshold frequency meaning that electrons flow from the cathod to the anode.
B. However the red light has a lower frequency then the treshold frequency meaning it doesn't have enough energy to break the work force and leave the metals surface therefore resulting in no photoelectric current

Reply 3

Cinna21

13

Original post by Aleprechaun

A. The blue light has a higher frequency then the threshold frequency meaning that electrons flow from the cathod to the anode.
B. However the red light has a lower frequency then the treshold frequency meaning it doesn't have enough energy to break the work force and leave the metals surface therefore resulting in no photoelectric current