Question

A. Blue light has higher energy than red light. Write 3 - 4 sentences comparing these electromagnetic waves with respect to the following properties: wavelength, frequency, and speed.
b. When a certain amount of blue light and red light shine on a metal surface, only blue light produces an electric current. Write 3 - 4 sentences describing how an increase in the intensity of each light will affect the amount of current produced. How does quantification help explain these observations?

Answer 1

PART A)

As we know that energy of light depends on its wavelength and frequency as following formula

$E = \frac{hc}{\lambda} = h\nu$

now we know that wavelength of blue light is less than the red light so here energy of blue light will be more

also we know that

$\nu = \frac{c}{\lambda}$

so here if wavelength is smaller for blue light so its frequency will be high and the speed of both light will be same in same medium

PART B)

Since we know that frequency of blue light is more than red light as well as wavelength of blue light is less than the wavelength of blue light so here blue light will have more energy

When blue light and red light strike the metal surface then due to more energy of blue light it will release some loosely bonded electrons from metal surface which will contribute in current.

here if we increase the intensity of light then the number of photons that contain the blue light of certain energy will be more and that will contribute more current

So here quantification help as we know that due to quantization only certain frequency or energy will lead to eject electron so all colours will not give this current

Answer 2

Explanation:

• For a:

The relationship between energy and frequency is given by Planck's equation, which is:

$E=h\nu$         ......(1)

where, h = Planck's constant

E = energy of the light

$\nu$ = frequency of light

We also know that:

$\nu=\frac{c}{\lambda}$

Putting the value of frequency in above equation:

$E=\frac{hc}{\lambda}$     ......(2)

We are given:

Energy of blue light is higher than Red light.

From relation 1, energy is directly related to frequency of the light. So, higher the energy, higher will be the frequency.

From relation 2, energy is inversely related to wavelength of the light. So, higher the energy, lower will be the wavelength.

Thus, blue light has higher energy, higher frequency and lower wavelength as compared to red light which has lower energy, lower frequency and higher wavelength.

• For b:

If the frequency of the light is more than the threshold frequency, it would be able to emit electrons and increase in intensity would result in more number of photons and hence, more number of electrons.

Whereas, if the frequency of the light is less than the threshold frequency, it would be not be able to emit electrons and increase in intensity would not result in more number of photons and hence, no electrons will be emitted.

Thus, the frequency and energy of blue light is more than the red light.