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प्रश्न
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.
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उत्तर
In a transformer with Ns secondary turns and Npprimary turns, induced emf or voltage Es is:
`E_s = -N_s (dphi)/dt`
Back emf = Ep =`-N_p(dphi)/(dt)`
EP = VP
Es = Vs
Thus, Vs = `-N_s (dphi)/()dt`… (1)
`V_p =-N_p (dphi)/dt ... (2)`
Dividing equations (i) and (ii), we obtain
`(V_s)/(V_p) = N_s/N_p`
If the transformer is 100% efficient, then
`i_p v_p = i_s v_s` = Power (p)
Thus, combining the above equations,
`i_p/i_s = v_s/v_p = N_s/N_p`
Or,
`V_s = (N_s/N_p)V_p and I_s = (N_p/N_s) I_p`
If Ns > Np, then the transformer is said to be step-up transformer because the voltage is stepped up in the secondary coil.
No, the transformer does not violate the principal of conservation of energies. This can be easily observed by the following equation:
`V_s I_s =V_pI_p`
Power consumed in both the coils is the same as even if the voltage increases or current increases, their product at any instant remains the same.
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संबंधित प्रश्न
Name two factors on which the magnitude of an induced e.m.f. in the secondary coil depends.
On which type of current do transformers work?
In a transformer, the frequency of A.C. voltage ______.
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The power supply to the primary coil of a transformer is 200 W. Find
(i) Current in primary coil if the e.m.f. supply to it is equal to 220V.
(ii) The number of turns in the primary coil is equal to 80 and that in secondary is 800. What is the transformation ratio?
(iii) Name the type of transformer.
(iv) What will be the output voltage?
(v) What is the current in the secondary coil for an ideal transformer?
(vi) What is the output power?
(vii) Is output and input power equal?
(viii) Compare the current flowing in a secondary coil and in a primary coil.
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The self-inductance of a closely wound coil of 200 turns is 10 mH. Determine the value of magnetic flux through the cross-section of the coil when the current passing through the coil is 4 mA.
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