Question on A level Physics,, (related to the waves)?

Question

Light of wavelength of 2.1 * 10^-7 m is incident on a metal whose work function is 2.8 * 10^-19 J.
What is the maximum kinetic energy of the electrons released from the metal ?
What is their maximum speed ?

Answer 1

The equation you need to use is

E = h * f

where h= plancks constant
and f is the frequency of the light ( f = speed of light / wavelength)

Then the maximum kinetic energy is this E - the work function

The maximum speed is found by rearranging
maximum Kinetic energy = (1/2) * m * v^2

where m is the mass of an electron
and v^2 is the speed squared

I will leave you to look up the constants and put numbers into a calculator.

Answer 2

wavelength= y(say)....lamda!
planck's constant=h=6.625*10^(-34)

so max K.E= hy (i.e dat electron absorbs da whole energy of dat 'photon')

so, => max.K.E= h*y( solve it) !!!!

1/2 . m. v^2 = max.K.E

WHER DA SPEED IS 'v',m=mass...... u vil get ur answer!!!!

Answer 3

as above