## Current I Questions

1. (a) Distinguish between natural and forced convection currents

(b) Draw the cross-section of a basic solar heating panel that uses heat from the sun to warm

water which flows through pipes

(b) Explain the following as regards to the solar heater:-

(i) Why the pipe is made of copper

(ii) How the green house effect occurs and aids the working of the panel

2. State two advantages of generating an alternating current (a.c) to direct current (d.c) in a

power station.

3.  The table below shows results obtained in an experiment to determine the internal resistance

of a cell

 V(V) 0.4 0.5 0.6 0.7 ecolebooks.com 08 1.3 R() 0.45 0.65 0.80 1.05 1.40 2.4 1/V (V-1) 1/R(-1)

i. Complete the table for values of 1/V and 1/R giving your answers to 3 d.p

ii. Plot a graph of 1/V against 1/R

iii. Use the graph to determine the e.m.f E and the internal resistance r of the cell given that

E = r 1

V R (4mks)

## Current I Answers

1.  (a) natural convection – involves change in density of the fluid with temperature, whereas

forced convection involves the mixing of hot and cold part of the fluid though some

external stirring, like a fan or pump  (2mks)

‘ (c) (i) Copper is a good conductor of heat; hence water gets warmed faster

(ii) The glass cover does not allow the radiant heat form inside the panel to escape since this

heat as lower energy than that from the sun. This heat continues being trapped inside

and the temperature increases, thus boosting the heating of the eater

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