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प्रश्न
Explain the construction and working of the transformer.
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उत्तर
Construction: It consists of two coils of primary and secondary coils insulated from each other and wound on a soft iron core as shown in fig. (a). Input is applied across the primary coil, and output is taken across the secondary coil.
Notations:
P1, P2: Primary coil
S1, S2: Secondary coil
There are two types of transformers:
- Step-up transformer: In this, the number of turns in the primary coil is less than the number of turns in the secondary coil. The primary coil is made up of thick wire, and the secondary coil is made up of thin wire.
- Step-down transformer: Here the number of turns in the primary coil is greater than that in the secondary coil. The secondary coil is made up of thick wire, and the primary coil is of thin wire.
Working: When an AC voltage is applied to the primary coil, the current through the coil goes on changing. Hence the magnetic flux through the core also changes. As this changing magnetic flux is linked with both coils, an emf is induced in each coil. The amount of magnetic flux linked with the coil depends upon the number of turns of the coil.
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संबंधित प्रश्न
Derive an expression for e.m.f. and current in terms of turns ratio
Express the turn ratio in terms of voltages.
Mention various energy losses in transformer device
The teachers of Geeta’s school took the students on a study trip to a power generating station, located nearly 200 km away from the city. The teacher explained that electrical energy is transmitted over such a long distance to their city, in the form of alternating current (ac) raised to a high voltage. At the receiving end in the city, the voltage is reduced to operate the devices. As a result, the power loss is reduced. Geeta listened to the teacher and asked questions about how the ac is converted to a higher or lower voltage.
1) Name the device used to change the alternating voltage to a higher or lower value. State one cause for power dissipation in this device.
2) Explain with an example, how power loss is reduced if the energy is transmitted over long distances as an alternating current rather than a direct current.
3) Write two values each shown by the teachers and Geeta.
How is the e.m.f. across primary and secondary coils of a transformer related with the number of turns of the coil in them?
Why is the core of a transformer laminated?
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……… energy is converted into …………energy by an electric motor.
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Name two kind of energy loss in a transformer. How is it minimized?
Describe briefly and two energy losses, giving the reasons for their occurrence in actual transformers ?
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Describe briefly, with the help of labelled diagram, working of a step-up transformer.
A step-up transformer converts a low voltage into high voltage. Does it not violate the principle of conservation of energy? Explain.
What is the turns ratio i.e., transformer ratio, ns: np, in an ideal transformer which in-creases ac voltage from 220 V to 33000 V?
State the principle of a transformer.
Can a transformer be used with direct current source? Give reason.
Why is the core of a transformer made of soft iron?
Name three losses of energy in a transformer. How are they minimized?
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Explain step up and step down transformer?
Transformer works on ______.
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Mention the various energy losses in a transformer.
A step-up transformer has 300 turns of primary winding and 450 turns of secondary winding. A primary is connected to 150 V and the current flowing through it is 9A. The current and voltage in the secondary are
The output power in step-up transformer used in practice is ______.
Assertion: A transfonner cannot work on D.C. supply.
Reason: D.C. changes neither in magnitude nor in direction.
A transformer works on the principle of ______.
A transformer is essentially an a.c. device. It cannot work on d.c. It changes alternating voltages or currents. It does not affect the frequency of a.c. It is based on the phenomenon of mutual induction. A transformer essentially consists of two coils of insulated copper wire having different numbers of turns and wound on the same soft iron core.
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The value of current in the bulb is ______.
Name one electrical device which works on Faraday's law of electromagnetic induction principle.
The primary coil of a transformer has 800 turns and the secondary coil has 8 turns. It is connected to a 220 V ac supply. What will be the output voltage?
A step-down transformer connected to an ac mains supply of 220 V is made to operate at 11 V, 44 W lamp. Ignoring power losses in the transformer, what is the current in the primary circuit?
1 MW power is to be delivered from a power station to a town 10 km away. One uses a pair of Cu wires of radius 0.5 cm for this purpose. Calculate the fraction of ohmic losses to power transmitted if
- power is transmitted at 220 V. Comment on the feasibility of doing this.
- a step-up transformer is used to boost the voltage to 11000 V, power transmitted, then a step-down transfomer is used to bring voltage to 220 V. (ρCu = 1.7 × 10–8 SI unit)
A transformer operating at primary voltage 8 kV and secondary voltage 160 V serves a load of 80 kW. Assuming the transformer to be ideal with purely resistive load and working on unity power factor, the loads in the primary and secondary circuit would be:
The magnetic flux through a coil perpendicular to its plane is varying according to the relation Φ = (5t3 + 4t2 + 2t - 5) Weber. If the resistant of the coil is 5 ohm, then the induced current through the coil at t = 2 sec will be ______.
Magnetic flux Φ in weber in a closed circuit of resistance 10Ω varies with time Φ (sec) as Φ = 6t2 - 5t + 1. The magnitude of induced current at t = 0.25s is ______.
An iron rod of 0.2 cm2 cross-sectional area is subjected to a magnetising field of 1200 Am-1. If the susceptibility of iron is 599, then the magnetic flux produced is ______.
The primary coil having NP turns of an ideal transformer is supplied with an alternating voltage VP. Obtain an expression for the voltage VS induced in its secondary coil having NS turns.
Mention two main sources of power loss in real transformers.
The primary coil of a transformer has 60 turns whereas its secondary coil has 3000 turns.
If a current of 5A flows in the primary coil, how much current will flow in a load in the secondary coil? State the assumption you have made regarding the transformer, in this calculation.
Derive the equation for a transformer.
What type of transformer is used in a mobile phone charger?
In an ideal transformer, the turns ratio is \[\frac {N_p}{N_s}\] = \[\frac {1}{2}\]. The ratio Vs : Vp is equal to (the symbols carry their usual meaning) ______.
A step down transformer connected to an AC mains supply of 220 V is made to operate at 11 V, 44 W lamp. Ignoring power losses in the transformer, what is the current in the primary circuit?
When is an emf induced in the neighbouring coil?
On the basis of winding, what are the two types of transformers?
How is the laminated soft iron core made?
Why is soft iron used in the core?
Assuming no flux leakage, which coils does the changing flux thread through?
Which law relates the changing flux to the EMF induced in both coils?
What do \[V_s\] and \[V_p\] represent?
For an ideal transformer with \[\frac{V_s}{V_p}=3\], what is \[\frac{I_p}{I_s}\]?
