Solution - Extra Explaining Questions - ELECTROMAGNETISM

ELECTROMAGNETISM

1. Explain why transformer are used to reduce the current passing through the transmission cables of the National Grid

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The transformer (Step –up) reduces the current passing through the transmission cables of the National Grid so as to reduce the energy wasted (Power Loss) by heating up the cables.

2.   Explain why transformer does not work using a d.c. supply. Why is an a.c. supply necessary to make a transformer work?

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According to Faraday Law of Electromagnetism that says “wherever there is change of magnetic flux (linking the coils) e.m.f is induced, so if the d.c is supplied to the primary coil of the transformer the magnetic field is constant (No change of magnetic flux). Then no potential difference (voltage) induced in the secondary coil.

3.  Explain why a bicycle lamp attached to the to the dynamo does not light when the.....  CONTINUE READING

FRICTION FORCE AT INCLINED PLANE

Consider the diagram below, a mass of body sliding down the incline plane

At constant speed a = 0m/s²

F_k = mgsinθ

R = mgcosθ

But:

Fk = μ_kR – make μ_k subject

μ_k = F_k/R

μ_k = mgsinθ/mgcosθ

μ_k = sinθ/cosθ

μ_k = Tanθ

Therefore, at constant speed coefficient of ..  CONTINUE READING

Cooling Effect of Evaporation

What is evaporation?

Evaporation is the gradual change of state from liquid to gas that occurs at the surface of the liquid

Evaporation occurs when particles escape from a liquid. This happen even when the temperature is lower than the boiling point.

Factors affecting evaporation

i.     Temperature

An increase of temperature increases the rate of evaporation

ii.    Surface area

A larger surface area allows more particles to leave the liquid hence the larger the surface area the higher rate of evaporation..  CONTINUE READING

Extra Explaining Questions - ELECTROMAGNETISM

ELECTROMAGNETISM

1. Explain why transformer are used to reduce the current passing through the transmission cables of the National Grid

2.   Explain why transformer does not work using a d.c. supply. Why is an a.c. supply necessary to make a transformer work?

3.  Explain why a bicycle lamp attached to the to the dynamo does not light when the bicycle is stationary?

4.   A student is trying to test a transformer using battery. Explain why the voltmeter connected to the secondary coil reads 0 V?

5.   A wire is made to move through a magnetic field so that a potential difference is induced across its ends. State two ways in which the...  CONTINUE READING