WorksheetsIX-A TRANSFORMERS
Total questions: 23
Worksheet time: 2hrs 42mins
What is the equation for finding the output voltage in a simple transformer
output voltage X input voltage =turns on input coil X turns on output coil
output voltage / input voltage = turns on output coil / turnds on input coil
input voltage + turns on input coil = output voltage + turns on output coil
The transformer above has an input current of 2 A and an output current of 1 A. Find the power through the transformer.
300 W
175 W
220 W
110 W
What type of transformer is used to increase the voltage from power stations.
Step-down transformer
Step-up transformer
Why transformers work with A.C. current but not D.C.
A.C current produces changing magnetic field
D.C current produces changing magnetic field
D.c current is very weak
Which place uses 11,000 V
Schools
Heavy industry
Light industry
Offices and shops
Which of the following does not change in a transformer
current
voltage
frequency
all of the above
A transformer transforms
voltage
current
power
frequency
Why a transformer cannot raise or lower the voltage of a D.C. supply
there is no need to change the D.C. voltage
a D.C. circuit has more losses
Faraday`s laws of electromagnetic induction are not valid since the rate of change of flux is zero
none of the above
Material used for construction of transformer core is usually:
wood
copper
aluminium
silicon steel
In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of:
less than 15 A
more than 15 A
15 A
none of the above
A step-down transformer changes 240 V a.c. to 12 V a.c. . There are 600 turns on the primary coil. How many turns are on the secondary coil?
20
30
600
12000
The diagram shows a working transformer.
Which statement is correct?
the input voltage is d.c.
the input voltage is greater than the output voltage
the input voltage is less than the output voltage
the input voltage is the same as the output voltage
Which statement about the action of a transformer is correct?
An e.m.f. is induced in the secondary coil when an alternating voltage is applied to the primary coil.
An e.m.f. is induced in the secondary coil when there is a steady direct current in the primary coil.
The current in the secondary coil is always larger than the current the primary coil.
The voltage in the secondary coil is always larger than the voltage in the primary coil.
Electrical energy is transmitted at highvalternating voltages.
What is not a volid reason for doing this?
At high voltage, a.c. is safer than d.c.
For a given power, there is a lower current with a higher voltage.
There is a smaller power loss at higher voltage and lower current.
The transmission lines can be thinner with a lower current.
A magnet is moved towards a coil of insulated wire. A voltmeter connected across the coil shows a positive reading.
What produces a higher reading on the voltmeter?
moving the magnet away from the coil at the same speed
moving the magnet away from the coil at a slower speed
moving the magnet towards the coil at a faster speed
moving the magnet towards the coil at a slower speed
A _________ magnetic field can induce an e.m.f in a ________.
moving ; insulator
moving ; conductor
stationary ; conductor
stationary ; insulator
___________ voltage can be increased or decreased using a ___________.
D.C. ; coil
A.C ; coil
A.C ; transformer
D.C ; transformer
When coils are magnetically linked , so that a changing ___________ in one cause an induced e.m.f in the other, this is called ___________.
current ; mutual induction
current ; electromagnetic induction
voltage ; mutual induction
voltage ; electromagnetic induction
All transformers ____________some energy.
reserve
waste
need
What action can damage a transformer?
connecting it to an a.csupply
connectingit to an electrical supply
putting a magnet near it
connecting it to a d.c supply
Asuming that the transformer on the right has an efficiency of 100 percent.
Calculate the supply voltage and the current in the input coil.
150 V ; 0.5 A
200 V ; 0.2 A
300 V ; 0.07 A
100 V ; 0.7 A
Which statement(s) about the action of a transformer is correct?
An e.m.f is induced in the secondary coil when alternating voltage is applied to the primary coil.
An e.m.f is induced in the secondary coil when there is a steady direct current in the primary coil.
The current in the secondary coil is always larger than the current in then primary coil.
The voltage in the secondary coil is always than the voltage in then primary coil.
power = ________X__________
resistace ; voltage
voltage ; current
current ; resistace
resistance ; energy transformed
