Advertisements
Advertisements
प्रश्न
Derive the equation for a transformer.
Advertisements
उत्तर
Let NP and Ns be the number of turns of the primary and secondary coils. Let Φ be the magnetic flux linked per turn.
Φp = NpΦ
= Total magnetic flux linked with the primary coil at certain instant,
Φs = NsΦ
= Total magnetic flux linked with the secondary coil at a certain instant.
By Faraday and Lenz's laws,
Induced emf in the primary coil (ep) is given by
`e_p = -(dphi_p)/dt`
= `-N_p(dphi)/dt` ...(i)
emf induced in the secondary coil (es) is
`e_s = -(dphi_s)/dt`
= `-N_s(dphi)/dt` ...(ii)
Dividing equation (ii) by equation (i),
`e_s/e_p = N_s/N_p` ...(iii)
The ratio `N_s/N_p` is called the turn ratio.
For an ideal transformer,
Input power = Output Power
epIp = esIs
`e_s/e_p = I_p/I_s` ...(iv)
From equations (iii) and (iv),
`e_s/e_p = N_s/N_p = I_p/I_s` ...(v)
APPEARS IN
संबंधित प्रश्न
Draw a labeled diagram of a step-down transformer.
A group of students while coming from the school noticed a box marked "Danger H.T. 2200 V" at a substation in the main street. They did not understand the utility of a such a high voltage, while they argued, the supply was only 220 V. They asked their teacher this question the next day. The teacher thought it to be an important question and therefore explained to the whole class.
Answer the following questions:
(i) What device is used to bring the high voltage down to low voltage of a.c. current and what is the principle of its working ?
(ii) Is it possible to use this device for bringing down the high dc voltage to the low voltage? Explain
(iii) Write the values displayed by the students and the teacher.
Express the turn ratio in terms of voltages.
What type of current is transmitted from the power station?
Name two factors on which the magnitude of an induced e.m.f. in the secondary coil depends.
You are required to make an electromagnet from a soft iron bar by using a cell, an insulated coil of copper wire and a switch. (a) Draw a circuit diagram to represent the process. (b) label the poles of the electromagnet.
State two ways through which the strength of an electromagnet can be increased.
For what purpose are the transformers used? Can they be used with a direct current source?
What is the function of a transformer in an a.c. circuit? How do the input and output powers in a transformer compare?
The input and output voltage of a transformer are 220 V and 44 V respectively. Find: the turns ratio.
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.
An a.c generator generates an emf 'ε' where ε = 314 Sin (50πt) volt. Calculate the frequency of emf ε.
Why is the core of a transformer made of soft iron?
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.
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.
A step-down transformer reduces the supply voltage from 220 V to 11 V and increase the current from 6 A to 100 A. Then its efficiency is
In a series resonant RLC circuit, the voltage across 100 Ω resistor is 40 V. The resonant frequency ω is 250 rad/s. If the value of C is 4 µF, then the voltage across L is
Explain the construction of 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 ______.
Which among the following, is not a cause for power loss in a transformer?
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.
A power transmission line feeds input power at 2300 V to a step down transformer with its primary windings having 4000 turns. The number of turns in the secondary in order to get output power at 230 V are ______.
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 voltage across the secondary coil 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 ______.
Define a Transformer.
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 transformer is used ______
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?
The line that draws power supply to your house from street has ______.
- zero average current.
- 220 V average voltage.
- voltage and current out of phase by 90°.
- voltage and current possibly differing in phase `phi` such that `|phi| < pi/2`.
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:
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 ideal transformer converts 220 V a.c. to 3.3 kV a.c. to transmit a power of 4.4 kW. If primary coil has 600 turns, then alternating current in secondary coil is ______.
Mention two main sources of power loss in real transformers.
The large scale transmission of electrical energy over long distances is done with the use of transformers. The voltage output of the generator is stepped-up because of ______.
Efficiency of transformer is the ratio of ______.
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?
Explain why core of a transformer is always laminated.
For what purpose are the transformers used?
A 12 V, 60 W lamp is connected to a 220 V AC supply using an ideal transformer. Find the primary current.
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 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?
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 ______.
In an ideal transformer, the turns ratio is `N_p/N_s = 1/2`. The ratio Vs : Vp is equal to (the symbols carry their usual meaning):
