law of radiation using a photoelectric cell 4th year right now

Experiment No. 3

Title: To study the inverse square law of radiation using a photoelectric cell

Aim:

To verify the inverse square law of radiation intensity using a photoelectric cell and a light source.

Apparatus Required:

• Photoelectric cell

• Light source (lamp or LED)

• Ammeter (micro-ammeter)

• Ruler or scale

• Variable power supply

• Light intensity measuring setup (optional)

Theory:

According to the inverse square law, the intensity of light or radiation is inversely proportional to the square of the distance from the source:

 

$$I \propto \frac{1}{r^2}$$

I∝r21​

The photocurrent (I) generated by a photoelectric cell is proportional to the light intensity falling on it. Hence:

 

$$I_{\text{current}} \propto \frac{1}{r^2}$$

Icurrent​∝r21​

Where r is the distance between the light source and the photocell.

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🧪 Procedure:

1. Set up the apparatus in a dark room to minimize external light interference.

2. Place the photoelectric cell on a fixed base and connect it to an ammeter.

3. Position the light source at a distance r from the photocell.

4. Switch on the lamp and note the photocurrent from the ammeter.

5. Vary the distance in equal intervals (e.g., 10 cm, 15 cm, 20 cm…)

6. Record the corresponding current at each distance.

7. Plot a graph of current (I) vs.

   $\frac{1}{r^2}$r21​ and analyze linearity.

Observation Table: