Section 6 Electricity Flashcards
What is current
The rate of flow of charge
What is a coulomb
The amount of charge that passes in 1 second when the current is one ampere
What is the equation to find coulombs, when using current and time
Charge in coulombs =current × time taken
(Change in) Q = I × (change in) t
Coulombs = current × time taken
What is used to measure current in a circuit
An ammeter (set up in series)
What is potential difference
Work done in moving a unit charge between the points
What equation is used to find potential difference when given work done and charge
V = W ÷ Q
Pd = work done ÷ charge
Volts = joules ÷ coulombs
What is used to measure potential difference in a circuit
A voltmeter (must be parallel to the component)
What is resistance
A measure of how difficult it is to get a current to flow
What equation is used for finding resistance, when given potential difference and current
R = V ÷ I
Resistance = potential difference ÷ current
Ohms = volts ÷ amps
What is ohms law
Provided the physical conditions, the current through an ohmic conductor is directly proportional to the potential differences across it
What does it mean if the gradient is shallower on an I-V graph
The component has a higher resistance
What does an I-V graph of an ohmic conductor look like
A positive straight line directly proportional
What does an I-V graph of a filament lamp look like
A curve that starts steep but gets shallower as the voltage rises
What does an I-V graphics diode look like
An exponential graph from the origin ( must have a threshold voltage (forward bias))
What is resistivity
How much a particular material resists current flow ( including the structure of the material and environmental factors)
What is the equation for resistivity when given resistance cross sectional area and length
Rho = ( R×A ) ÷ L
Resistivity = (resistance×cross sectional area) ÷ length
Ohmic meters = (ohms×metres(2))÷ metres
What are semiconductors
A group of materials that aren’t as good at conducting electricity as metals
What is a thermistor
A component with a resistance that depends on it’s temperature
What is special about ntc thermistors ( negative temperature coefficient)
Resistance decreases as the temperature goes up
What is a superconductor
When a material cools below their critical temperature, their resistivity disappears entirely. Without resistance none of the electrical energy is turned into heat.
What are the uses for superconductors (3)
Power cables that transmit energy without the loss of power
Really strong electromagnets ( medicine and make trains)
Electronic circuits that work really fast with minimal energy loss
What is power?
The rate of energy transfer and measured in watts (where 1 watt is equivalent to 1 joule per second)
What is the equation for power when given pd and current
P = I × V
Power = current × pd
Watts = amps × volts
What is the equation for power when given voltage and resistance
P = V(squared) ÷ R
Power = voltage ( squared) ÷ resistance
Watts = volts(squared) ÷ ohms
What is the equation for power when given current and resistance
P = I(squared) × R
Power = current (squared) × resistance
Watts = amps (squared) × resistance
How can you figure out energy
By substituting P = E ÷ t into the power equations dependant on the variable given.
What are the rules for voltage when in a series curcuit
V(total) = v1+ V2 + V3 …
What the rules for resistance when in series
R(total) = r1 + r2 + r3…
What are the rules for current when in parallel
Current is split at each junction so:
I = i1 + i2 + i3 … ( At each junction explicitly
Splits as a ratio comparatively to each component on each branch
What are the rules for resistance when in parrallel
1/R(total) = 1/R1 + 1/R2 + 1/R3 …
What are the rules for current when in series
Stays the same throughout
What are the rules for voltage when in a parallel circuit
Stays the same throughout
