Advertisements
Advertisements
Question
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.
Advertisements
Solution
Principle − It works on the principle of electromagnetic induction. When current in one circuit changes, an induced current is set up in the neighbouring circuit.
Construction
Working
-
Alternating emf is supplied to the primary coil PP’. The resulting current produces an induced current in secondary.
-
Magnetic flux linked with primary is also linked with the secondary. The induced emf in each turn of the secondary is equal to that induced in each turn of the primary.
Let
EP − Alternating emf applied to primary
nP − Number of turns in the primary
`(dø)/dt - `Rate of change of flux through each turn of primary coil
∴`E_p = - n_p (dø)/dt .......... (1)`
Es− Alternating emf of secondary
ns − Number of turns in secondary
∴`E_s = - n_s (dø)/dt .......... (2)`
Dividing equation (2) by (1),
`E_s/E_p = n_s/n_p = k`
For step-up transformer, K > 1
∴ Es > Ep
-
According to law of conservation of energy,
-
Input electrical power = Output electrical power
EpIp = EsIs
∴ `E_s/E_p = I_p/I_s`
APPEARS IN
RELATED QUESTIONS
State two factors on which the magnitude of induced e.m.f. depend.
Describe briefly and two energy losses, giving the reasons for their occurrence in actual transformers ?
State the principle of a transformer.
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
Explain the construction of transformer.
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 ______.
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.
If the secondary coil has a greater number of turns than the primary, ______.
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 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?
