P6

Question 1

What do the symbols for power supplies look like?

Answer 1

Look at notes for better diagram

All supply current to circuit

-l i-
Cell

-lilili- or -li——li-
Battery of cells

—o o—
Power supply

—o+ -o—
Dc power supply

—o~o—
C power supply

—[G]—
Generator

Question 2

What do the symbols for resistors look like?

Answer 2

Look at notes for better ones

resistors all used to control current

—[ ]—
Fixed resistor

—[^]—
Variable resistor

—[ _/]—
Thermistor

—([ ])—
LDR

Question 3

What do the symbols for meters (volt and amp) look like?

Answer 3

-(A)-
Ammeter

-(V)-
Voltmeter

Used to measure current and voltage

Question 4

What do the symbols for fuses look like?

Answer 4

—[——]—
Fuse

Question 5

What do the symbols for switch, lamp and earth look like?

Answer 5

Just look on notes i can’t bother

Question 6

What does the resistance in an LDR look like?

Answer 6

Current voltage graph -> straight line though origin

Low R -> high light
High R -> low light

Question 7

What does the resistance in a thermistor look like?

Answer 7

Curved line (look at notes)
DOESN’T FOLLOW OHMS LAW -> LINE IS NOT STRAIGHT

Resistance down -> temp up

Question 8

T or F: combined resistance of 2 resistors in parallel is more than that of entire resistor by itself

Answer 8

False: combined resistance is less that that of either resistor

Question 9

What is the equation for total resistance of 2 resistors in parallel?

Answer 9

1/R(total) = 1/R1 (resistor 1) + 1/R2 (resistor 2)

NOT EQUAL TO RT= R1 + R2

Question 10

What is the advantage of connecting lamps in parallel?

Answer 10

The lamps will be able to be turned on or off using their own switched

If one lamp stops working, the other will continue to work

Voltage/energy will be equal to each lamp -> same brightness

Question 11

What is an input transducer?

Answer 11

Converts energy from one form to another

Ex: Thermistor: heat -> sound
Ex: LDRS: light -> sounds

Question 12

Describe how NTC thermistors and LDR are used as input transducers

Answer 12

Ex: thermistor
-> semiconductors used as sensors

LOOK AT NOTES FOR DIAGRAM

Resistance in V(T):
High at low temp -> high voltage -> less current
Low at high temp -> low voltage -> more current

Less or more voltage/current triggers a reaction -> ex: high temp -> low voltage/high current -> heater turns off

Ex: LDR
Resistance in LDR:
High at low light -> high voltage -> less current
Low at high light -> low voltage -> more current

Question 13

What is the equation for power?

Answer 13

P -> power (watts)
I -> current
V -> voltage

P = IV

Question 14

What is the equation for energy?

Answer 14

E -> energy (joules (J))
I -> current
V -> voltage
t -> time

E = IVt

Question 15

What are some examples of electrical hazards?

Answer 15

Damaged insulation:
Insulation -> plastic sheath that covers wires
Damaged -> wire showing and if touched could lead to electric shock (interferes with nerve signals -> maybe death)

Overheating of cables:
High current -> risk of overheating -> too much energy
= electrical fires

Damp conditions:
Water -> conductor
Electricity can electrocute via water -> high risk in bathrooms, dishwashers, etc.

Excess current:
Overwhelming plugs
Too many components in one socket - increased risk of fire

Question 16

What is a fuse?

Answer 16

A thin, metal wire with a low melting point that melts when a high current produces too much heat -> prevents fires and breaks circuit

Usually a glass cylinder with a wire

FUSE PROTECTS CIRCUIT NOT YOU

Question 17

What is a trip switch?

Answer 17

Consumer box (where electricity enters building) -> current too high -> switch automatically turns off -> stops the flow of current

Question 18

How does a circuit breaker work?

Answer 18

Electricity flows through metal contacts -> high current -> stronger electromagnet -> pulls iron catch -> spring pulls metal contacts apart -> circuit breaks

Question 19

How do you choose an appropriate fuse rating (3A, 13A, 15A) ?

Answer 19

1. Figure out current
2. Choose fuse rating high than the current (one size up)

Question 20

What is an alternate equation for current (hint: p and v)?

Answer 20

Current = power/mains voltage

Question 21

What is mains electricity?

Answer 21

Electricity generated by power stations and transported around the country

Usually an ac supply -> has live and neutral not Pos and neg

Question 22

Explain the structure of a three-pin plug

Answer 22

Stocket:
Longer rectangle -> earth (earths appliances in metal cases)
Other -> neutral (0 voltages -> go out) and live ( alternate Pos and neg voltage -> go in)

Wires:
Live -> brown
Neutral -> blue
Earth -> green and yellow

Question 23

What is the structure/materials used in electric cables? Why?

Answer 23

Copper wires -> good conductors, made of many thin strands to keep it flexible

Plastic covering -> prevent a short circuit -> wires don’t touch
Plastic is good insulator, tough and flexible

Question 24

Why is earth/earthing necessary? How?

Answer 24

For appliances with metal cases, if the live wire touches the case it could lead to electrocution -> poses a great safety hazard

Earth wire reduces risk -> a low resistance path to earth
When the current is going though both the earth and live wires -> fuse metals and cuts off supply