P6 Flashcards
What do the symbols for power supplies look like?
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
What do the symbols for resistors look like?
Look at notes for better ones
resistors all used to control current
—[ ]—
Fixed resistor
—[^]—
Variable resistor
—[ _/]—
Thermistor
—([ ])—
LDR
What do the symbols for meters (volt and amp) look like?
-(A)-
Ammeter
-(V)-
Voltmeter
Used to measure current and voltage
What do the symbols for fuses look like?
—[——]—
Fuse
What do the symbols for switch, lamp and earth look like?
Just look on notes i can’t bother
What does the resistance in an LDR look like?
Current voltage graph -> straight line though origin
Low R -> high light
High R -> low light
What does the resistance in a thermistor look like?
Curved line (look at notes)
DOESN’T FOLLOW OHMS LAW -> LINE IS NOT STRAIGHT
Resistance down -> temp up
T or F: combined resistance of 2 resistors in parallel is more than that of entire resistor by itself
False: combined resistance is less that that of either resistor
What is the equation for total resistance of 2 resistors in parallel?
1/R(total) = 1/R1 (resistor 1) + 1/R2 (resistor 2)
NOT EQUAL TO RT= R1 + R2
What is the advantage of connecting lamps in parallel?
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
What is an input transducer?
Converts energy from one form to another
Ex: Thermistor: heat -> sound
Ex: LDRS: light -> sounds
Describe how NTC thermistors and LDR are used as input transducers
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
What is the equation for power?
P -> power (watts)
I -> current
V -> voltage
P = IV
What is the equation for energy?
E -> energy (joules (J))
I -> current
V -> voltage
t -> time
E = IVt
What are some examples of electrical hazards?
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
What is a fuse?
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
What is a trip switch?
Consumer box (where electricity enters building) -> current too high -> switch automatically turns off -> stops the flow of current
How does a circuit breaker work?
Electricity flows through metal contacts -> high current -> stronger electromagnet -> pulls iron catch -> spring pulls metal contacts apart -> circuit breaks
How do you choose an appropriate fuse rating (3A, 13A, 15A) ?
- Figure out current
- Choose fuse rating high than the current (one size up)
What is an alternate equation for current (hint: p and v)?
Current = power/mains voltage
What is mains electricity?
Electricity generated by power stations and transported around the country
Usually an ac supply -> has live and neutral not Pos and neg
Explain the structure of a three-pin plug
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
What is the structure/materials used in electric cables? Why?
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
Why is earth/earthing necessary? How?
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
