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State Faraday's law of electromagnetic induction - Leaving Cert Physics - Question 12(c) - 2007
Question 12(c)
State Faraday's law of electromagnetic induction. Describe an experiment to demonstrate Faraday's law. A resistor is connected in series with an ammeter and an ac ... show full transcript
Worked Solution & Example Answer:State Faraday's law of electromagnetic induction - Leaving Cert Physics - Question 12(c) - 2007
Step 1
State Faraday's law of electromagnetic induction.
Answer
Faraday's law of electromagnetic induction states that the induced electromotive force (emf) in a circuit is proportional to the rate of change of magnetic flux through the circuit. In equation form, it can be stated as:
ext{emf} = - rac{d ext{Φ}}{dt}
where ( \text{emf} ) is the induced electromotive force, ( \text{Φ} ) is the magnetic flux, and ( t ) is time. The negative sign indicates the direction of the induced emf according to Lenz's law.
Step 2
Describe an experiment to demonstrate Faraday's law.
Answer
Apparatus
- Coil
- Magnet
- Galvanometer or equivalent
Arrangement
- Connect the coil to a galvanometer.
Procedure
- Move the magnet towards the coil.
Observation
- The faster the movement of the magnet, the greater the deflection of the galvanometer, which indicates an induced voltage.
Step 3
What is the effect on the current flowing in the circuit? Justify your answer.
Answer
When the resistor is replaced with a coil, the current flowing in the circuit is reduced. This occurs because:
- The coil has a self-inductance, which opposes the change in current flow through it due to Lenz's law. When the coil is introduced, it generates a back emf that counters the applied voltage from the power supply.
- Since the resistance of the circuit does not change, the back emf effectively reduces the net voltage applied across the circuit, resulting in a decrease in the current according to Ohm's law, ( I = \frac{V}{R} ), where ( I ) is current, ( V ) is voltage, and ( R ) is resistance.