Electricity (1) Flashcards
current-
potential difference-
resistance-
current- flow of electrical charge
potential difference-
driving force that pushes charges / the amount of energy transferred points in a circuit
resistance- how difficult it is for charge to flow
resistance of a wire RP-
- attach a crocodile clip to the wire level with 0cm on the ruler
- attach a second clip 10 cm away
- close the switch and record the current and Pd across the wire
- open the switch and move the wire another 10cm along
- record the new readings and repeat with different length wires
- calculate resistance
Improvements to the resistance of a wire RP (2)-
Use thinner crocodile clips to have more precise measurements along the ruler
Limit the wire heating up by letting it cool down between tests and having a lower current by using a variable resistor
factors affecting resistance (4)
length- longer = more resistance
thickness- thicker = less resistance as more open space
temperature- higher temperature = higher resistance
material- denser material = higher resistance
fuse-
LED-
resistor-
variable resistor-
diode-
LDR-
thermistor-
fuse- breaks the circuit if there is a fault
LED- light emitting diode
resistor- increases resistance in a circuit
variable resistor- the resistance can be changed
diode- has high resistance in the opposite direction of current flow
LDR- Light-dependent resistor, in bright light, resistance falls
thermistor- in hot conditions, resistance drops
Resistance and IV characteristics and graph shape
Ohmic conductor-
Bulb-
Diode-
Ohmic conductor- resistance is constant (straight line gradient) as current and voltage increase proportionally
Bulb- resistance increases with temperature (curve) so current decreases
Diode- resistance depends on the direction of current flow (very high resistance in the reverse direction) (flat line then extremely high gradient)
series circuits (PD, current and resistance)
parallel circuits (PD, current and resistance)
series circuits-
PD is shared between components. If the resistance of one component is greater, the voltage will be greater
Current is the same at all points but decreases with more components added as there is more resistance
Resistance adds up so adding more resistors increases total resistance
parallel circuits-
PD across each branch is equal to the power supply. Adding more components to one branch splits voltage in the same way as in a series circuit
Current is split between the branches of the circuit. This depends on the resistance of each branch. Adding more components increases current
Resistance decreases when adding more resistors in parallel as there’s an increased capacity in the circuit
Current-time graph for an AC
Current-time graph for a DC
curve alternating between positive and negative voltages
The positive and negative values indicate the direction of the current flow
On a voltage-time graph, this would appear as a straight horizontal line at a constant voltage.
Electricity in the home:
Is mains power AC or DC?
What voltage and frequency is it?
live wire and colour-
neutral wire and colour-
earth wire and colour-
fuse-
Insulation-
AC
230V, 50hz
live wire- brown, supplies the alternating potential difference from
the mains supply
neutral wire- blue, completes the circuit, current flows through it
earth wire- green and yellow, protects the wiring and is a safety
feature. If there’s an electrical surge, the fuse breaks the current passes along the earth wire and earthed
fuse- thin wire with a determined resistance that melts when a certain current is exceeded, preventing the casing from becoming live
Insulation- doesn’t conduct electricity so safe touch
How is The National Grid optimised-
What voltage does electricity travel through the grid at-
Distributes electricity across the UK
It uses a high PD and low current to decrease energy loss
Step-down and step-up transformers change the PD
It travels through the grid at 40 000V
stepped down to 230V for safe domestic use
Static electricity-
How do you receive a static shock-
build-up of static caused by friction of insulating materials
electrons move from the negatively charged object to the positively charged object creating static build up
static shock is caused by the static charges transferring to the person touching them
how are electrical sparks created
When there is a big enough potential difference between the oppositely charged objects, the air molecules become ionised which makes them conductive so electrons can flow through them
This causes a spark
What direction do electric field lines go from a positive charge and negative charge
arrows point away at a perpendicular angle for positive
arows point towards at a perpendicular angle for a negative charge
What are power ratings
how much energy an appliance uses
(circuit symbols)
fuse-
LED-
resistor-
variable resistor-
diode-
LDR-
thermistor-
fuse- box with a line running through the centre
LED- diode with two arrows pointing away from it on the right side
resistor box with lines either side
variable resistor- box with an arrow going through the middle from left to right
diode- triangle with a line next to it in a circle
LDR- resistor in a circle with two arrows pointing at it from the left side
thermistor- box with a diagonal line through the middle with a flat line (-/)
explain the trends between voltage and resistance, and current and resistance
as resistance increases, voltage increases as there are more collisions between the electrons and positive metal ions which transfers energy
as resistance increases, current decreases as there are more collisions between the electrons and positive metal ions which decreases the rate of flow of charge
Series of units (metres, 8 )
nm µm mm cm m km Mm Gm
nanometer, micrometer, millimeter, centimeter, meter, kilometer, megameter, gigameter
Units for potential difference (2)
1 V = 1 J/C
How is the potential difference created in a battery in a circuit
One side is positive and one is negative, this creates a potential difference
What is ohms law
Voltage and Current are proportional across an ohmic conductor
What must the circuit diagram include when measuring IV characteristics
Variable power supple (arrow going through it)
What direction do electrons flow from a power supply
from the positive terminal to the negative
