The Irish physicist George Stoney is most famous for introducing the term electron - Leaving Cert Physics - Question 12 - 2022

To demonstrate the photoelectric effect, we can perform the following experiment:

Apparatus: Electroscope, zinc plate, UV lamp.

Method:

1. Connect the zinc plate to the electroscope.
2. Shine the UV lamp on the zinc plate for a specific duration.
3. Observe the deflection of the electroscope’s needle.

Observation: If the frequency of the UV light is above the threshold frequency, the needle will deflect, indicating that electrons are being emitted from the zinc plate.

If the frequency of the incident light is below the threshold frequency, the photoelectric effect does not occur. This means that no electrons are emitted from the surface of the metal, and the electroscope will show no deflection, as there are insufficient energy photons to release the electrons.

To calculate the wavelength, we can use the formula:

Where:

• $c$ is the speed of light (approximately 3 x 10^8 m/s).
• $f$ is the frequency (6.5 x 10^{14} Hz).

Plugging in the values:

The energy of a photon can be calculated using the formula:

Where:

• $E$ is the energy,
• $h$ is Planck’s constant ($6.63 imes 10^{-34} ext{ Js}$),
• $f$ is the frequency (6.5 x 10^{14} Hz).

Substituting the values:

Electrons are produced in an X-ray tube through the process of thermionic emission, where a heated filament (cathode) releases electrons. These free electrons are then directed toward the target.

Electrons are accelerated in an X-ray tube using a high voltage. The high voltage creates a strong electric field that propels the electrons toward the anode at high speeds.

Tungsten has a high melting point and a high specific heat capacity, making it suitable as a target in an X-ray tube as it can withstand the intense heat generated during electron bombardment.

Lead can be used to ensure that the X-rays do not escape from the X-ray tube. Its dense and absorbent nature effectively shields against X-ray radiation.