Advertisements
Advertisements
Question
Derive an expression for e.m.f. and current in terms of turns ratio
Advertisements
Solution
Expression for e.m.f and current :
- Let,`phi` be the magnetic flux linked per turn with both the coils at certain instant ‘t’
- Let ‘NP and ‘NS’ be the number of turns of primary and secondary coil,
NP`phi` = magnetic flux linked with the primary coil at certain instant ‘t’
NS`phi` = magnetic flux linked with the secondary coil at certain instant ‘t’ - Induced e.m.f produced in the primary and secondary coil is given by,
`e_p=-(dphi_p)/dt=-N_p(dphi)/dt`….(1)
`e_s=-(dphi_s)/dt=-N_s(dphi)/dt`......(2) - Dividing equation (2) by (1),
`e_s/e_p=N_s/N_p`….(3)
Equation (3) represents equation of transformer.
The ratio `N_s/N_p` is called turns ratio (transformer ratio) of the transformer - For an ideal transformer,
Input power = Output power - `e_pI_p=e_sI_s`
`e_s/e_p=I_p/I_s`.................(4) - From equation (3) and (4),
`e_s/p_p=N_s/N_p=I_p/I_s`
APPEARS IN
RELATED QUESTIONS
Explain the construction and working of the transformer.
A transformer converts 240 V AC to 60 V AC. The secondary has 75 turns. The number of turns in primary are _______.
(A) 600
(B) 500
(C) 400
(D) 300
State the principle of the step-down transformer and its working.
Find the ratio of primary and secondary currents in terms of turn ratio in an ideal transformer.
State the principle of transformer working with the help of a diagram
The adjacent diagram shows a coil would around a soft iron bar XY. (a) State the polarity at the end X and Y as the switch is pressed. (b) Suggest one way increasing the strength of electromagnet so formed.
State two factors on which the magnitude of induced e.m.f. depend.
Explain the significance of Lenz’s law to show the conservation of energy in electromagnetic induction.
For what purpose are the transformers used? Can they be used with a direct current source?
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 transformer is used in ______ current circuits.
What is the function of a transformer in an a.c. circuit? How do the input and output powers in a transformer compare?
Name two kind of energy loss in a transformer. How is it minimized?
The primary coil of a transformed has 800 urns and the secondary coil has 8 turns. It is connected to a 220 V a.c. supply. What will be the output voltage?
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?
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.
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.
The input and output voltages of a transformer are 220 V and 44V respectively. Find the current in input circuit if the output current is 2 A.
What is the ideal transformer?
What is the function of a step-up transformer?
Name three losses of energy in a transformer. How are they minimized?
(i) Draw a clear labelled diagram of an electric bell.
(ii) Explain in brief, its working.
(iii) What material is used for the core of an electric bell? State the reason.
Copy the given diagram of a transformer and complete it. Name the parts A and B. Name the part you have drawn to complete the diagram. What is the material of this part? Is this transformer a step-up or step-down? Give reason.
A transformer lowers e.m.f. 220 V to 12 volts. If the number of turns in primary are 8800, how many turns are in secondary coil?
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 ______.
What is Transformer?
Describe the construction and working of a transformer with a neat labelled diagram.
Devices which is used to convert high alternating current to low alternating current is ______.
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
What are step-up and step-down transformers?
Mention the various energy losses in a transformer.
Give the advantage of AC in long distance power transmission with an illustration.
Assertion: A transfonner cannot work on D.C. supply.
Reason: D.C. changes neither in magnitude nor in direction.
A 100% efficient transformer has 100 turns in the primary and 50 turns in its secondary coil. If the current in the secondary coil is 6 A, then the current in the primary coil is ______.
A power transmission line feeds input power at 2300 V to a stepdown transformer with its primary windings having 4000 turns. What should be the number of turns in the secondary in order to get output power at 230 V?
A transformer works on the principle of ______.
For an ideal step-down transformer, the quantity which is constant for both the coils is ______.
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 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 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?
A transformer consisting of 300 turns in the primary and 150 turns in the secondary gives output power of 2.2 kW. If the current in the secondary coil is 10 A, then the input voltage and current in the primary coil are ______.
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 ______.
Efficiency of transformer is the ratio of ______.
What is a transformer?
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?
A 12 V, 60 W lamp is connected to 220 V AC via an ideal transformer. Find the primary current.
An ideal transformer converts 170 V a.c. to 1.70 KV a.c. to transmit a power of 3.4 KW. If primary coil has 500 turns then alternating current in secondary coil is ______.
