Physics Questions and Answers

Eddy currents are produced by the varying flux cathode, the iron core of an equipment thus reducing efficiency due to power consumption. It can be reduced by laminating the core by breaking up the path of eddy current or by increasing the resistance of the core
Usage of insulated soft iron wire is to reduce hysteresis loss
Usage of low resistance wire (thick wire) is to reduce I2R loss
Usage of thick wire is to reduce leakage heat loss due to leakage of magnetic flux
Thus the correct answer is to use high resistance wire or thin wire

From Hoke's Law, F = ke, K = Constant of Force

For he first case, Force = mg,

= 0.8 × 10 = 8N

∴ 8 = k × 0.04

k = $\frac{8}{0.04}$

= $\frac{200N}{m}$

Since K is constant

For the second case, F = ke

F = 200 × e

∴ e = $\frac{F}{200}$

= $\frac{16}{200}$

= 0.08m

Power of a lens = $\frac{1}{f}$

f = focal length

f = $\frac{1}{p}$

= $\frac{1}{5}$

= 0.2m

V = fλ

λ = $\frac{v}{f}$

= $\frac{3 \times 10^8}{600 \times 10^3}$ = 500m

= 5 × 10²m

N.B 600KHz Frequency = 600 × 10³Hz

Power is the time rate of doing work

i.e power = $\frac{\text{energy}}{\text{time}}$

Since energy = mgH

∴ power = $\frac{mgH}{t}$

= $\frac{50 \times 10 \times 5}{t}$

= 500W