ELECTRICAL

CELLS

100

State what is a cell.

It consists of one negative and one positive terminal.

200

State the purpose of a cell.

Converting chemical energy to electrical energy.

300

What is the difference between primary and secondary cells?

Primary cells are not rechargeable, and the secondary cells are rechargeable.

400

The two faults of the carbon-zinc cell  are  and what do they produce?

local action - corrosion

polarization - insulator

500

A battery has an open-circuit voltage of 9V and a closed-circuit voltage of 6V with a current of 2 A flowing. What is the internal resistance?

r = 1.5-ohms

ILLUMINATION

100

Define illumination

The amount of light falling on a working plane.

200

What formula is used for illumination when the individual is at an angle?

E = (I/d²) Cos 0

300

What is the formula for luminous intensity?

I = E x d²

400

Explain cosine Law

The closer the light source is to the working plane, the brighter the luminous intensity, but the less surface area is covered.

500

Calculate the illumination falling on a working plane 2m from the light source of 64cd

E = I/ d²

E = 64/2²

E = 64/ 4

E = 16 Lux

TYPE OF CURRENT

100

What are the types of voltage?

Direct Current & Alternating Current

200

What is the difference between AC and DC voltage?

Direct voltage maintains constant polarity and constant magnitude, whereas alternating current is the opposite.

300

 Two advantages of DC supply.

žCan be used to magnetized and charge a capacitor

400

Two characteristics of the AC supply and define them

Any two

Frequency                Period

Cycle                       Instantaneous value

RMS vale

Average value

500

A sine valve has a peak value of 100V. Calculate the V_RMS & Vavg values

V_RMS = 0.707 x Vp                Vavg = 0.637 x Vp

V_RMS = 0.707 x 100              Vavg = 0.637 x100

V_RMS = 70.7V                        Vavg = 63.7V

RESISTORS

100

Define a resistor

This is an electrical device that imparts resistance into a circuit.

200

Name the 2 groups of resistors.

Fixed and Variable

300

State 2 types of fixed resistor and one type of variable resistor

Fixed - carbon composition, film, 

Variable: rheostat, potentiometer

400

What do the colours represent on the resistor?

1^st band - first digit

2^nd band - 2nd digit

3^rd band - multiplier

4^th band - tolerance

500

Decode the resistor of colours red, blue, red and gold

2600 - ohms +/- 15%

SYMBOLS

100

What quantity does the symbol below represent?

                        Ω

Unit for resistance.

200

 What quantity uses the symbol "P"

Power

300

What is the unit symbol for the quantity of electric charge?

C

400

What is the unit symbol for energy?

J

500

What is the formulae for power using the symbols

P = IV

P =I²R

P = V²/R