May'15

Question 1

Describe the structure of a transformer.

Answer 1

Consists of two separate coils of wire wound on the same iron core

Question 2

What is the equation used when dealing with transformers?

Answer 2

Vs/Vp= Ns/Np

which is secondary voltage/primary voltage = Number of secondary turns/ number of primary turns

Question 3

What are the equations for efficiency?

Answer 3

Effieciency= output power or energy/ input power or energy x100%

Question 4

What can affect the size of an induced voltage when a wire is moved within a magnetic field?

Answer 4

Move the wire faster between the poles
Use a stronger magnet
Use more conductor

Question 5

How are electrons arranged in a conductor?

Answer 5

They contain electrons which are free to move throughout the structure

Question 6

How are electrons arranged in a insulator?

Answer 6

The electrons are tightly bound and cannot move.

Question 7

Describe a series circuit.

Answer 7

When components are connected in line, we say they are connected in series.

Question 8

What is the unit of current?

Answer 8

Amperes (A)

Question 9

How do you measure current?

Answer 9

Make a gap in the circuit and connect an ammeter. The reading on the ammeter is the current.

Question 10

Describe a parallel circuit.

Answer 10

When components are connected so that there is more than one path for the current, we say they are connected in parallel.

Question 11

What is meant by voltage in an electrical circuit?

Answer 11

It is the electrical energy supplied by the battery to make the electrons move around the circuit.

Question 12

How do you measure voltage?

Answer 12

Use two extra wires to connect to a voltmeter in parallel with the component.

Question 13

How is resistance in an electrical circuit measured?

Answer 13

An ohmeter is connected directly across the component which must be disconnected from the circuit.

Question 14

What is the unit for resistance?

Answer 14

Ohms

Question 15

What is the equation for Ohm’s Law?

Answer 15

Resistance= voltage/ current which is R= V/ I

Question 16

What is the equation involving current, charge and time?

Answer 16

current= charge/ time which is: I= Q/t

Question 17

What is alternating current?

Answer 17

A.C goes up and down and is produced from the main supply.

Question 18

What is direct current?

Answer 18

D.C ——————— and is produced from a battery.

Question 19

What is the unit of energy?

Answer 19

Joules, J.

Question 20

What is the unit of power?

Answer 20

Watt, W

Question 21

What is the equation involving energy, power and time?

Answer 21

energy= power x time which is: E= Pt

Question 22

What are the three parts of an electronic system in order?

Answer 22

The input, the process, the output.

Question 23

What type of device are a thermistor, LDR and switch?

Answer 23

Input

Question 24

What happens to the resistance of a thermistor when the temperature changes?

Answer 24

High temperature= Low resistance

Low temperature= High resistance

Question 25

What happens to the resistance of an LDR when the light levels change?

Answer 25

Bright light= Low resistance | Dark light= High resistance

Question 26

What is an appropriate input device for a loudspeaker and heating system?

Answer 26

Microphone and Thermistor

Question 27

What is an appropriate input device for an automatic lamp and a lighting circuit?

Answer 27

LDR and Switch

Question 28

What is the energy change in an output device?

Answer 28

Electrical energy-------> another form of energy.

Question 29

What type of devices are a loudspeaker, buzzer, lamp, LED and electric motor?

Answer 29

Output

Question 30

What is an appropriate output device for a warning light, a fan and smoke alarm?

Answer 30

LED, Motor and Buzzer

Question 31

What does the NOT gate look like?

Answer 31

Continuous line input and output------- | triangle with circle at the end

Question 32

What does the AND gate look like?

Answer 32

2 lines at start (input A and B) and one line at the end (output) half circle

Question 33

What does the OR gate look like?

Answer 33

2 lines at start (input A and B) and one line at the end (output) triple curved shape

Question 34

What does the truth table for a NOT gate look like?

Answer 34

Input | Output 0 | 1 1 | 0

Question 35

What does the truth table for an AND gate look like?

Answer 35

``` Input A and B | Output 0 0 0 1 0 0 0 1 0 1 1 1 ```

Question 36

What does the truth table for an OR gate look like?

Answer 36

Input A and B | Output 0 0 0 1 0 1 0 1 1 1 1 1

Question 37

What is meant by specific heat capacity?

Answer 37

The amount of energy need to raise 1kg of a solid by 1'C. | Measured in J-1Kg'C-1

Question 38

What is the equation for specific heat capacity?

Answer 38

Energy= specific heat capacity x mass x change is temperature which is: Eh= cm (Delta)T

Question 39

What is the equation for work done?

Answer 39

Work done= force x displacement | which is: Ew= Fs

Question 40

What is the equation for kinetic energy?

Answer 40

Kinetic energy= 1/2 x mass x velocity^2 | which is: Ek= 1/2 mv^2