SKH Li Fook Hing Secondary School
Physics
EM11
Name:_________________________ Class No.:_____
Group No.:_______
Date of Experiment: ___________
EM11 Experiment: Transformer
Objective: To investigate the factors affect the voltage and current in the primary and secondary
coils in transformer.
Apparatus: Low voltage power (a.c.), PVC-covered copper wire, 60+120 turns coil, 120+240
turns coil, double C-core, 0-5A a.c. ammeter (2), “12V, 24W” lamp, CRO,
connecting wires.
Procedure and results:
1. Construct a transformer with a 60+120 turn coil as the primary coil
2.
and wind a coil of 20 turns round the C-coil as the secondary coil as
shown in the figure.
Connect the 60 turns and common terminals of the coil to the a.c.
terminals of the a.c. supply. Set the a.c. power supply to 3V. Connect
the secondary to a CRO to measure the peak voltage of the secondary coil.
(The marked value in the panel is the root mean square value of the applied voltage.)
Move the secondary coil at different position on the core and notice the induced e.m.f. on the
CRO.
PQ1.
3.
Is there any difference of the induced e.m.f. when the secondary coil is wound round
the C-core at different position?
Construct a transformer with 60 turns coil as the primary and a 120 turns coil as the secondary.
Apply 3V a.c. to the primary and measure the primary voltage on a CRO. Then, measure the
secondary voltage by the CRO. Change the secondary coil to 240 turns and measure the
secondary voltage again. Tabulate the results:
No. of turns in primary= 60
peak voltage in primary=
No. of turns in secondary
120 turns
Peak voltage in secondary Vs/V
Ns
Turn ratio
Np
Voltage ratio
PQ2.
Vs
Vp
What do you notice about the turn ratio and voltage ratio?
p.1
__________V
240 turns
SKH Li Fook Hing Secondary School
Physics
EM11
Name:_________________________ Class No.:_____
4.
Date of Experiment: ___________
Connect a “12V, 24W” lamp across the secondary coil and find out how the secondary voltage
is affected.
PQ3.
5.
Group No.:_______
How is the secondary voltage affected?
Connect an a.c. ammeter to the primary coil and an a.c.
ammeter to the secondary coil. Set the voltage of the primary
coil at 3V. Find out the currents in the primary and secondary
coil with different number of turns in the coils.
No. of turns in primary Np
60 turns
60 turns
120 turns
120 turns
No. of turns in secondary Ns
120 turns
240 turns
120 turns
240 turns
Current in primary Ip / A
Current in secondary Is / A
Turn ratio
Ns
Np
Current ratio
PQ4.
6.
Is
Ip
What is the relationship between the turn ratio and current ratio?
Estimate the power delivered to the primary and the power supplied to the secondary coil.
(Power = voltage x current)
No. of turns in primary= 60
peak voltage in primary=
No. of turns in secondary coil
120 turns
Current in primary coil Ip / A
Current in secondary coil Is / A
Voltage in primary coil Vp / V
Voltage in secondary coil Vs / V
Power delivered to the primary coil
Power supplied to the secondary coil
Efficiency of the transformer
p.2
___________V
240 turns
SKH Li Fook Hing Secondary School
Physics
EM11
Name:_________________________ Class No.:_____
6.
Group No.:_______
Date of Experiment: ___________
Connect the CRO to the primary coil and sketch the
waveform displaced in the space provided. Then,
Connect the CRO to the secondary coil and sketch
in the same space. Note the starting traces of the
primary and secondary. Compare the phase
difference between the primary and secondary
voltages.
PQ6.
What is the phase difference between the
primary and secondary voltages? Explain
briefly.
Questions:
1.
Under what conditions is the voltage ratio equal to the turn ratio?
2.
Under what condition is the current inversely proportional to the turn?
3.
Discuss the energy loss in transformer.
Reference: Further Physics Book II p.155-p.158, New Way Physics Book 3 p.306-p.309
p.3