Resistance of the bulb in open circuit in Electric Current – Class 10 Science Experiment

Chapter Name: Electric Current

Activity Name: Resistance of the bulb in open circuit in Electric Current

Activity Description:

Resistance of the bulb in open circuit in Electric Current - Class 10 Science Experiment

This experiment aims to measure the resistance of a bulb in an open circuit using a multi-meter.

The resistance of the bulb is measured again after allowing current to flow through it for a few minutes, and the difference in the two readings is noted. The experiment demonstrates the relationship between the resistance of the bulb and its temperature.

Required Items:

  • Multi-meter (ohm-meter function)
  • Bulb
  • Circuit components (not specified)

Step by Step Procedure:

  1. Set the multi-meter to the ohm-meter function and select the 20K Ω range.
  2. Place the leads of the multi-meter on the terminals of the bulb and note the resistance reading. If the reading is 0.00 or 1 or the actual resistance of the bulb, record it. If the reading shows OL (overloaded) or 1, try a higher mode (e.g., 200K Ω or 2M Ω), and if the reading is nearly 0, try a lower mode (e.g., 2K Ω or 200 Ω).
  3. Connect the circuit components as shown in figure 13.
  4. Switch on the circuit and allow current to flow through the bulb for a few minutes.
  5. Measure the resistance of the bulb again using the same procedure as before and note the value in your notebook.

Experiment Observations:

  • Resistance of the bulb in open circuit (before current flow).
  • Resistance of the bulb after current flows through it for a few minutes.


  1. Ensure the multi-meter is set to the correct mode and range before measuring the resistance.
  2. Handle the bulb and circuit components with care to avoid damage.
  3. Take safety precautions when dealing with electricity, such as wearing insulated gloves if required.

Lesson Learnt from Experiment:

The experiment demonstrates that the resistance of the bulb increases when current flows through it. This increase in resistance is attributed to the heating of the filament inside the bulb. The relationship between resistance and temperature is established, showing that for a constant potential difference between the ends of a conductor, the resistance varies with temperature.

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