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प्रश्न
Describe the construction and working of a transformer with a neat labelled diagram.
Explain the working of a transformer with a neat labelled diagram.
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उत्तर
Principle: It is based on the principle of mutual induction, i.e., whenever the magnetic flux linked with a coil changes, an e.m.f is induced in the neighbouring coil.
Construction: A transformer consists of two sets of coils, primary P and secondary S, insulated from each other. Coil P is called the input coil, and coil S is called the output coil. The two coils are wound separately on a laminated soft iron core.
Working: When an alternating 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 e.m.f. is induced in each coil. The amount of the magnetic flux linked with the coil depends upon the number of turns of the coil.
Let Φ be the magnetic flux linked per turn with both coils at a certain instant ‘t’. NP and NS be the number of turns of the primary and secondary coils, respectively.
Then at the instant t, the magnetic flux linked with the primary coil ΦP = NPΦ and with the secondary coil ΦS = NSΦ.
The induced emf in the primary and secondary coils will be:
ep = `-(d Phi_p)/(dt) = -N_p(d Phi)/(dt)` ...(1)
es = `-(d Phi_s)/(dt) = -N_s(d Phi)/(dt)` ...(2)
Dividing equation (2) by (1),
∴ `e_s/e_p = N_s/N_p` ...(3)
Equation (3) represents the equation of the transformer.
The ratio `N_s/N_p` is called the turns ratio (transformer ratio) of the transformer.
For an ideal transformer,
Input power = Output power
∴ ePIP = eSIS
∴ `e_s/e_p = I_p/I_s` ....(4)
From equations (3) and (4),
`e_s/e_p = N_s/N_p = I_p/I_s`
Notes
Students should refer to the answer according to their questions.
APPEARS IN
संबंधित प्रश्न
Explain the construction and working of the transformer.
Derive an expression for ratio of e.m.f.s and currents in terms of number of turns in primary and secondary coil.
Derive an expression for e.m.f. and current in terms of turns ratio
A power transmission line feeds input power at 2200 V to a step-down transformer with its primary windings having 300 turns. Find the number of turns in the secondary to get the power output at 220 V.
Express the turn ratio in terms of voltages.
Find the ratio of primary and secondary currents in terms of turn ratio in an ideal transformer.
How much current is drawn by the primary of a transformer connected to 220 V supply when it delivers power to a 110 V − 550 W refrigerator?
Mention various energy losses in transformer device
Which coil of a step up transformer is made thicker and why?
Name two factors on which the magnitude of an induced e.m.f. in the secondary coil depends.
Complete the following sentence :
……… energy is converted into …………energy by an electric motor.
The following diagram in Fig. 10.44 shows a coil X connected to a sensitive centre –zero galvanometer G and a coil P connected to a battery through a switch S.
(a) Describe the observation when the switch S is (i) closed suddenly, (ii) then kept closed, (iii) finally opened.
(b) Name and state the law which explains the above observations.
How are the e.m.f in the primary and secondary coils of a transformer related with the number of turns in these coils?
The secondary windings of a transformer in which the voltage is stepped down are usually made of thicker wire than the primary. Explain why.
Why is the iron core of a transformer made laminated (thin sheets) instead of being in one solid piece?
A transformer is designed to work from a 240 V a.c. mains and to give a supply of 8 V to ring a house bell. The primary coil has 4800 turns. How many turns will be in the secondary coil?
The input and output voltage of a transformer are 220 V and 44 V respectively. Find: the turns ratio.
Describe, with the help of a suitable diagram, the working principle of a step-up transformer. Obtain the relation between input and output voltages in terms of the number of turns of primary and secondary windings and the currents in the input and output circuits.
State the underlying principle of a transformer. How is the large scale transmission of electric energy over long distances done with the use of transformers?
Describe briefly and two energy losses, giving the reasons for their occurrence in actual transformers ?
State the principle of working of a transformer. Can a transformer be used to step up or step down a d.c. voltage? Justify your answer.
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.
State the factors on which the frequency of the alternating e.m.f. depends.
Name three losses of energy in a transformer. How are they minimized?
A circular coil of 100 turns with a cross-sectional area of 1 m2 is kept with its plane perpendicular to the magnetic field of 1 T. The magnetic flux linkage is ______.
An ideal transformer has 100 turns in the primary and 250 turns in the secondary. The peak value of the AC is 28 V. The rms secondary voltage is nearest to ______
Explain step up and step down transformer?
Devices which is used to convert high alternating current to low alternating current is ______.
State whether true or false. If false, correct the statement.
A transformer can step up direct current.
In a transformer, the number of turns in the primary and the secondary are 410 and 1230 respectively. If the current in primary is 6A, then that in the secondary coil is
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What are step-up and step-down transformers?
A step-down transformer connected to the main supply of 220 V is used to operate 11V,88W lamp. Calculate
- Voltage transformation ratio and
- Current in the primary
The 300 turn primary of a transformer has resistance 0.82 Ω and the resistance of its secondary of 1200 turns is 6.2 Ω. Find the voltage across the primary if the power output from the secondary at 1600V is 32 kW. Calculate the power losses in both coils when the transformer efficiency is 80%
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
A 220 V input is supplied to a transformer. The output circuit draws a current of 2.0 A at 440 V. If the ratio of output to input power is 0.8, then the current drawn by primary winding 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 ______.
For an ideal step-down transformer, the quantity which is constant for both the coils is ______.
Read the following paragraph and answer the question:
Long distance power transmissions
The large-scale transmission and distribution of electrical energy over long distances is done with the use of transformers. The voltage output of the generator is stepped up. It is then transmitted over long distances to an area sub-station near the consumers. There the voltage is stepped down. It is further stepped down at distributing sub-stations and utility poles before a power supply of 240 V reaches our homes.
We need to step-up the voltage for power transmission, so that ______.
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.
The number of turns in the primary and secondary coils of an ideal transformer is 2000 and 50 respectively. The primary coil is connected to a main supply of 120 V and secondary coil is connected to a bulb of resistance 0.6 Ω.
The value of current in primary coil is ______.
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?
The primary winding of a transformer has 100 turns and its secondary winding has 200 turns. The primary is connected to an a.c supply of 120 V and the current flowing in its is 10 A. The voltage and the current in the secondary are ______.
A 60 W load is connected to the secondary of a transformer whose primary draws line voltage. If a current of 0.54 A flows in the load, what is the current in the primary coil? Comment on the type of transformer being used.
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:
In a transformer, number of turns in the primary coil are 140 and that in the secondary coil are 280. If current in primary coil is 4 A, then that in the secondary coil is ______.
The primary coil of a transformer has 60 turns whereas its secondary coil has 3000 turns.
If a 220 V ac voltage is applied to the primary coil, how much emf is induced in the secondary coil?
How do the input and output powers in a transformer compare? State the assumption made.
