Photo AI
In an experiment to demonstrate the photoelectric effect, a piece of zinc is placed on a gold leaf electroscope, as shown - Leaving Cert Physics - Question c - 2006
Question c
In an experiment to demonstrate the photoelectric effect, a piece of zinc is placed on a gold leaf electroscope, as shown. The zinc is given a negative charge causin... show full transcript
Worked Solution & Example Answer:In an experiment to demonstrate the photoelectric effect, a piece of zinc is placed on a gold leaf electroscope, as shown - Leaving Cert Physics - Question c - 2006
Step 1
Explain why the gold leaf deflects when the zinc is given a negative charge.
Answer
The gold leaf deflects when the zinc is given a negative charge due to electrostatic repulsion. When the zinc, which is a conductor, acquires a negative charge, it gains excess electrons. These negatively charged electrons repel each other, creating a repulsive force between the zinc and the gold leaf. Since both the zinc and the gold leaf become negatively charged, the same charges repel according to Coulomb's law. This leads to the observable deflection of the gold leaf away from the zinc.
Step 2
Ultraviolet radiation is then shone on the charged zinc and the gold leaf falls. Explain why.
Answer
When ultraviolet radiation is shone on the charged zinc, it provides enough energy to eject some of the electrons from the zinc surface. This process is known as the photoelectric effect. As the electrons are emitted, the overall negative charge on the zinc decreases. Consequently, the repulsive force on the gold leaf diminishes, allowing it to fall back towards its original position as the electrostatic repulsion is reduced.
Step 3
What is observed when the experiment is repeated using infrared radiation?
Answer
When the experiment is repeated using infrared radiation, the gold leaf does not collapse, and no significant change is observed. Infrared radiation does not possess enough energy to eject electrons from the zinc surface, thus failing to induce the photoelectric effect. As a result, the charge on the zinc remains unchanged, maintaining the electrostatic repulsion between the zinc and the gold leaf.
Step 4
Give one application of the photoelectric effect.
Answer
One application of the photoelectric effect is in automatic doors, where sensors detect the presence of a person and trigger the doors to open. Other applications include smoke alarms, photovoltaic cells, and various safety switches used in machines.