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What is a photon? (6) An investigation was carried out to establish the relationship between the current flowing in a photocell and the frequency of the light incident on it - Leaving Cert Physics - Question 8 - 2009
Question 8
What is a photon? (6) An investigation was carried out to establish the relationship between the current flowing in a photocell and the frequency of the light incid... show full transcript
Worked Solution & Example Answer:What is a photon? (6) An investigation was carried out to establish the relationship between the current flowing in a photocell and the frequency of the light incident on it - Leaving Cert Physics - Question 8 - 2009
Step 1
Step 2
Draw a labelled diagram of the structure of a photocell.
Answer
A typical photocell structure consists of:
- A cylindrical cathode (electrode) surrounded by a glass casing
- A wire anode (electrode)
- A vacuum region within the casing. Ensure each part is clearly labeled in the diagram for clarity.
Step 3
Step 4
What is the maximum speed of an emitted electron when light of wavelength 550 nm is incident on the photocell?
Answer
To find the maximum speed (v) of the emitted electron, use the equation for conservation of energy:
hf = rac{1}{2} mv^2 \\ \text{Where:} \\ - h = 6.6 \times 10^{-34} J s \\ - f = \frac{3 \times 10^{8} m/s}{550 \times 10^{-9} m} = 5.45 \times 10^{14} Hz \\ - m = 9.1 \times 10^{-31} kg \\ \text{Substituting values:}Calculating, we find:
Step 5
Explain why a current does not flow in the photocell when the frequency of light is less than 5.2 x 10^14 Hz.
Answer
A current does not flow in the photocell when the frequency of the incident light is below the threshold frequency because the energy of the incoming photons is insufficient to overcome the work function of the metal. Hence, no electrons are emitted.
Step 6
Draw a sketch of the graph obtained. How was the intensity of the light varied?
Answer
The graph should display intensity (I) on the y-axis against distance (or intensity) on the x-axis with a linear relationship illustrating increased current with increased light intensity. The intensity of light can be varied by changing the distance of the light source to the photocell or altering the light source power.
Step 7
What conclusion about the nature of light can be drawn from these investigations?
Answer
The investigations conclude that light has a quantized nature, demonstrating that it behaves as both a wave and a particle. The phenomenon of photoelectric effect showcases that light is made up of photons, or bundles of energy, reinforcing its particle-like properties. Thus, we can say that light has a corpuscular nature, while also exhibiting wave-like behavior.