2 Electricity Flashcards
Charge comes from…
electrons moving
Unit of Charge
Coulombs (C)
What is current
The rate of flow of charge
Unit of Current
Amperes (A) = C/s
1 Coulomb per second
Q =
Charge (C)
It
Current (A) x time (s)
When are the dangers of electrostatics
4 points
- Charges build up when 2 insulating materials rub against each other
- Electrons move from one surface to another
- (surfaces that gain electrons become negative, surfaces losing electrons become positive)
- you must ‘earth’ or ‘ground’ objects to lose charge as the electrons have a path to earth -> where they pread out
Why is earthing important for refuelling
a discharge of electrons results in a spark which can cause an explosion
Circuit Components
Draw an LDR
rectangle with 2 arrows going in
Light Dependent Resistor
Circuit Components
Draw a diode
triangle with line at pointy end
Circuit Components
Draw an LED
triangle with line at pointy end, 2 arrows pointing out of the triangle
Light emitting diode
Circuit Components
Draw a thermistor
rectangle with hockey stick
Circuit Components
Draw a thermistor
rectangle with hockey stick
Circuit Components
Draw a motor
circle with M
Circuit Components
Draw a fuse
rectangle with the wire going through it
(ONLY TIME WIRE GOES THROUGH RECTANGLE)
Circuit Components
Draw a variable resistor
reactangle with diagonal arrow going through it
Circuit Components
Draw a transformer
on either side of the wire (not going through the wire), 4 bumpy edges
Describe an experiment to investigate charging by friction
- rub both ends of a polythene rod with a cloth
- suspend the rod without touching the end, from a strand using a cradle and nylon thread
- take a rod of different insulating material and rub it with another cloth of the same material
- record any observations
- repeat with different materials and compare
Give the variables from the experiment
Independent - different rods material
Dependent - charge on rod
Controlled - 1. time spent rubbing rod
2. using same type of cloth
3. using same length of rod
Results from experiment
- When 2 insulating materials rub together - electrons pass from one insulator to another insulator
- polythene rod beomes negatively charged after being rubbed with cloth -> electrons move from cloth to rod
Current flows from…
positive -> negative
current along a wire with no junctions is …
constant
current at a junction is…
conserved
this means -> total current in = total current out
Unit of voltage (potential difference)
volts = j/c
joules/coumlob
ELECTRICITY
know the units for :
current =
charge =
resistance =
time =
potential difference =
power =
current = Ampere (A)
charge = coulomb (C)
resistance = ohm (Ω)
time = second (s)
potential difference = volt (V)
power = watt (W)
Explain how fuses protects the device or user in domestic appliances
Stop the flow of current by melting if the current is too high. So protecting sensitive components and people because if the components function at too higher temperature it can cause a fire.
Explain how circuit breakers protects the device or user in domestic appliances
breakers again break the circuit if current is too high.
Explain how insulation and double insulation protects the device or user in domestic appliances
prevent people from touching exposed wires and getting shocks.
Explain how earthing protects the device or user in domestic appliances
provides a low resistance path to the earth so if some one does come into contact with a current instead of flowing through them to the earth giving them a shock it flows through the earthing wire.
why a current in a resistor results in the electrical transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts
Resistance causes transfer of electrical energy to heat energy. Some components are designed to have a high resistance to make sure this happens, for example electrical heaters that have lots of resistors to ensure a high resistance so a lot of heat is produced.
Power =
P =
(watts)
current x voltage
I x V
(A) x (V)
what is a volt equivalent to
Joule/coulomb
J/C
how to pick which fuse is correct when given
current of fuse should be slightly higher than current in circuit - so if circuit heats up normally and fuse keeps breaking even though current isn’t too high - then fuse current is too low
fuse amps (3A, 5A, 13A)
Energy (J) =
potential difference (V) x current (A) x Time (s)
I x V x t
Alternating current:
describe the motion of the current
current constantly changes direction
Direct current:
describe the motion of the current
current flows in only one direction
is mains eletricity AC or DC supply?
what voltage, frequency and current?
AC
230V
50Hz
do batteries and solar cells supply AC or DC electricity?
how much would a typical battery supply
DC
1.5 V
why a series or parallel circuit is more appropriate for particular applications, including domestic lighting
Advantages of parallel circuits:
Components (e.g. bulbs) may be switched on/off independently.
If one component breaks, current can still flow through the other parts of the circuit.
Bulbs maintain a similar brightness.
Advantages of series circuits:
Fewer wires, cheaper and easier to assemble.
Uses less power
as voltage increases in a circuit, current also________
increases
the more components in a circuit, the _______ the current
lower
describe graph of wire, filament lamp, diode as graph shows how current varies with voltage
(resistance changed using variable resistor)
wire - directly proportionate
filament lamp - s curve
diode - horizontal line and sudden steep gradient
changing resistance in a circuit will _________ the current
decrease as V = IR
describe how resistance changes in an LDR
as light increases, resistance decreases
describe how resistance changes in a thermistor
as temperature increases, resistance decreases
how to check if there is current in a circuit
add lamp, if current is flowing, lamp will light up
current is the ….
rate of flow of charge
so I =
Q/t
Q =
Charge (C) =
I x t
electric current in solid metallic conductors is a flow of ….
negatively charged electrons - free to flow in metals so carry charge - negative electrons attracted to positive charges
why current is conserved at a junction in a circuit
At a junction current ‘splits’ to take both paths.
It comes back together when the paths meet again.
I1 = I2 + I3 +I4
how is voltage and current, resistance split in a series circuit?
voltage - split between components
current -same for each component
resistance - split between components
how is voltage and current split in a parallel circuit?
voltage - same for each component
current - split between branches
voltage =
energy transferred / charge
J/C
energy transferred (J) =
E =
charge (C) x voltage (V)
QV
conducting materials
Copper
Aluminium
Gold
Silver
Insulating Materials:
Glass
Air
Plastic
Rubber
Wood
