The following apparatus was used toa.Calculate the value of Plank's constantb.Prove inverse square law for intensity of lightc.None of thesed.Calculate charge to mass ratio of electrone.Measure strength of magnetic field produced due to Helmholtz coils

Your question seems to be incomplete as you haven't provided the details or image of the apparatus you're referring to. However, I can provide general steps on how to use common apparatus for each of the experiments you mentioned:

a. Calculate the value of Planck's constant:

• Use a LED of known wavelength.
• Measure the voltage across the LED when it just starts to glow.
• Repeat the process for LEDs of different wavelengths.
• Plot a graph of voltage against 1/wavelength.
• The slope of the graph gives the value of Planck's constant.

b. Prove inverse square law for intensity of light:

• Use a light source and a light sensor.
• Measure the intensity of light at different distances from the source.
• Plot a graph of intensity against the square of the distance.
• If the graph is a straight line, it proves the inverse square law.

c. None of these: Not applicable.

d. Calculate charge to mass ratio of electron:

• Use a cathode ray tube with a fluorescent screen.
• Apply a known electric field and magnetic field.
• Measure the deflection of the electron beam on the screen.
• Use the formula e/m = 2V/(B^2r^2) to calculate the charge to mass ratio.

e. Measure strength of magnetic field produced due to Helmholtz coils:

• Use a Hall probe or a magnetic field sensor.
• Place the probe or sensor at the center of the Helmholtz coils.
• Measure the magnetic field strength.
• Repeat the process for different currents through the coils.
• The magnetic field strength is directly proportional to the current.

Please provide more specific details if you're referring to a specific apparatus or experiment.