Starting with only the balmer series light (visible light), how could we ensure that the solar panels generate a current that mark can use for his power station? (it may to look at the electromagnetic spectrum from week 3): a. by gradually increasing the brightness (amount) of light that we shine on it. b. by gradually increasing the frequency of the light we shine on it. c. by gradually increasing the wavelength of the light that we shine on it.

The correct answer is (a).

Solar panels generate current using the principles of photoelectric emission, according to which, electrons are liberated from surfaces of certain substances when light of suitable frequency was allowed to fall on it. A photon of the incident radiation interacts with an electron of the panel and liberates it from the surface of the panel.

When the brightness of the light shining on the panel is increased, the intensity of the incident light increases. This means that the number of incident photons also increases. Since each photon has a probability of liberating one electron, as the number of incident photons  increase, the number of liberated electrons also increases proportionally. Since photoelectric current is the rate of flow of photo electrons,  the photo electric current increases with the increase in the intensity/ brightness of incident light.

If the frequency of light is increased, without increasing the brightness, the photoelectric current does not increase, since the number of incident photons remains the same. However, the liberated electrons exit the surface with greater kinetic energies. But since the number of electrons liberated remain the same, the photoelectric current remains unchanged irrespective of the fact that each electron may possess greater kinetic energy. The option b is incorrect.

Increasing the wavelength of the incident light, reduces the energy of the incident photons. This will result in the emitted electrons exiting electrons leave with lesser energy. However, if the brightness remains the same, there would be no change in the number of electrons and hence the photo electric current remains unchanged. Option (c) is also incorrect.

The correct option is (a). The required current can be generated by increasing the brightness of the incident light.