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Loudspeakers, d.c - Leaving Cert Physics - Question 10 - 2015
Question 10
Loudspeakers, d.c. motors and galvanometers are all based on the principle that a current-carrying conductor in a magnetic field experiences a force. Describe a lab... show full transcript
Worked Solution & Example Answer:Loudspeakers, d.c - Leaving Cert Physics - Question 10 - 2015
Step 1
Describe a laboratory experiment to demonstrate this principle.
Answer
To demonstrate the principle that a current-carrying conductor experiences a force in a magnetic field, a simple laboratory experiment can be conducted.
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Equipment Needed: A power supply, a flat coil of conducting wire (copper), a bar magnet, and a suitable support stand.
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Setup: Connect the coil to the power supply. Position the bar magnet such that its magnetic field lines are perpendicular to the plane of the coil.
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Execution: When the power supply is turned on, current will flow through the coil. Observe the coil's movement. Since the current-carrying conductor (the coil) is in the magnetic field of the bar magnet, it will experience a force and move or deflect.
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Observation: Measure the deflection angle of the coil with a protractor, showing the effect of the magnetic force on the conductor.
Step 2
Describe, with the aid of a labelled diagram, the principle of operation of the moving-coil loudspeaker.
Answer
The moving-coil loudspeaker operates based on electromagnetic induction. The components include a coil of wire, a permanent magnet, and a diaphragm. The process is as follows:
- Coil: Connected to an audio signal, the coil carries an AC current, producing a magnetic field around it.
- Magnet: The permanent magnet provides a stable magnetic field.
- Interaction: The interaction between the magnetic fields causes the coil to experience a force, which makes it move back and forth.
- Diaphragm: This coil is attached to a diaphragm that vibrates as the coil moves, producing sound waves corresponding to the audio signal.
Diagram: (not included, but should show the coil, magnet, diaphragm, and relevant connections).
Step 3
What is the principal energy conversion that takes place in a d.c. motor?
Answer
The principal energy conversion that takes place in a d.c. motor is from electrical energy to kinetic energy. The electrical energy supplied to the motor is converted into mechanical energy, which allows the motor to perform work.
Step 4
Step 5
Step 6
Calculate the maximum torque exerted by the motor.
Answer
To calculate the maximum torque exerted by the d.c. motor, use the formula:
egin{align*}
F &= B I L
&= 5.5 ext{ T} imes 1.2 ext{ A} imes 0.08 ext{ m}
&= 0.528 ext{ N}
ext{(length is converted from 8 cm to meters)}
ext{Torque} &= F imes r
&= 0.528 ext{ N} imes 0.08 ext{ m} imes 500 ext{ turns}
&= 21.12 ext{ N m}
ext{Maximum torque is approximately } 21.1 ext{ N m.}
Step 7
Explain how the galvanometer could be converted into a voltmeter of full-scale deflection 5 V.
Answer
To convert a galvanometer into a voltmeter of full-scale deflection 5 V:
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Place a resistor (R) in series with the galvanometer.
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Determine the required resistance using Ohm's law:
egin{align*} V &= IR \ R &= rac{V}{I} &= rac{5 ext{ V}}{0.01 ext{ A}} &= 500 ext{ Ω} ext{(to accommodate 10 mA deflection)} \ ext{Total resistance required} &= R_g + R
R_g &= 90 ext{ Ω (internal resistance)} ext{
Therefore,} R &= 500 ext{ Ω} - 90 ext{ Ω} = 410 ext{ Ω} ext{
This will allow the galvanometer to read up to full-scale deflection at 5 V.}