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  • (a) With the help of a labelled diagram, explain the working of a step-up transformer. Give reasons to explain the following : (i) The core of the transformer is laminated. (ii) Thick copper wire is used in windings. (b) A condu

(a) With the help of a labelled diagram, explain the working of a step-up transformer. Give reasons to explain the following :
(i) The core of the transformer is laminated.
(ii) Thick copper wire is used in windings.

(b) A conducting rod PQ of length 20\; cm and resistance 0.1\Omega  rests on two smooth parallel rails of negligible resistance AA{}' and CC{}'. It can slide on the rails and the arrangement is positioned between the poles of a permanent magnet producing uniform magnetic field B=0.4T. The rails, the rod and the magnetic field are in three mutually perpendicular directions as shown in the figure. If the ends A and C of the rails are short circuited, find the

(i) external force required to move the rod with uniformvelocity v=10cm/s, and

(ii) power required to do so.

 

 
 
 
 
 

Answers (1)

a) 

Transformer works on the principle of mutual induction.

\rightarrow whenever the current associated with the primary coil charges an emf is induced in the secondary coil.

A transformer in which the output (secondary) voltage is greater than its input (primary) voltage is called a step-up transformer.

The induced emf across the primary

e_p=-N_p\frac{d\phi}{dt}

The induced emf across the secondary

e_s=-N_s\frac{d\phi}{dt}

\frac{e_s}{e_p}=\frac{N_s}{N_p}

i)

Transformer cores are laminated to reduce the eddy current

ii)

Thick copper wires are used to reduce the heat loss

b)

i.

\\F=\frac{B^2vl^2}{R}=\frac{0.4^2\times0.1\times0.2^2}{0.1}\\\\=6.4\times10^{-3}N

ii.

P=\\F.v=6.4\times10^{-3}\times0.1=0.64\times10^{-3}W

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Safeer PP

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