P45 Electricity Flashcards
state the equation that links charge, current, and time
charge = current x time
Q = I x t
(C) (A) (s)
define potential difference
the force pushing charge around a circuit/ energy used to move charge around a circuit (work done)/ energy transferred per unit charge to move charge between two circuit points
the voltage/potential diff across two circuit points
also known as voltage
measured in volts using a voltmeter
state the equation linking potential diff, energy, and charge
energy = potential diff x charge
E = V x Q
(J) (V) (C)
describe how current moves through a parallel circuit
- the current is divided between two or more paths at the junction
- more current will move through the wire with fewer resistant components (resistor or bulb) as this is the path of least resistance
- ammeters on the path of least resistance will show a higher current reading
describe current and voltage in a series circuit
- current through each component is the same - all ammeters will have the same reading
- voltage across circuit is sum of voltages in all components
state the equation linking resistance, current, and potential diff
resistance = potential diff / current
R = V / I
(Ω) (V) (A)
describe a fixed resistor
- ohmic conductor as it follows Ohm’s law - the voltage is directly proportional to the current (provided all conditions eg. temp remain constant)
*maintains constant resistance regardless of potential diff - particles in a resistor give a constant obstruction to current
- current increases as potential diff increases - direct proportion
- shown on graph as straight diagonal line through the origin
describe a filament lamp
- resistance increases as potential diff increases
- filament wire heats up so particles move faster and more collisions happen between electrons in moving current+atoms - increased resistance
- current increases less for higher potential diff - shown on graph as initially straight line through origin then gradient becomes shallower (s shape curve)
describe a diode
- high resistance to negative potential diff so doesn’t allow current to flow
- resistance above 0.7V is constant and current can flow
- particles in a diode act as valves+ only allow charge to travel in one direction
- current is 0 until pd=0.7 then current is directly proportional to pd - shown on graph as flat line at 0 then gradient becomes very steep at 0.7
describe a thermistor
- resistance decreases as temp increases
- thermal energy helps particles line up/form regular arrangement so charge can move through more easily
- current increases as temp increases
- shown on graph as decreasing curve
describe a light dependent resistor
- resistance decreases as light intensity increases
- light energy helps particles line up/form regular arrangement so charge can move through more easily
- current increases as light intensity increases
describe the method for RP: how the length of wire affects resistance
- set up circuit: place a cell, ammeter+test wire in series then connect a voltmeter to places in the circuit before+after the test wire
- place jockey on test wire at length of 100cm
- measure the potential diff using voltmeter and current using ammeter
- calculate resistance = potential diff / current
- repeat steps for lengths 90cm-30cm in intervals of 10cm
describe sources of error, prevention and improvements for RP: how length of wire affects resistance
- wire gets hot which changes the temp of the wire:
start taking results at the longest length as wire would heat up less
connect resistance wire to the circuit by the jockey for the shortest possible time to minimise current flow
pause between readings to allow wire to cool down
alternative method - have resistance wire submerged in water to help regulate temp - results precision - improved by repeating experiment+ calculating mean results
describe the conclusion for RP: how length of wire affects resistance
- as the length of wire increases the resistance increases
- shown on graph as straight line passing through the origin
- the current flowing through the wire contains charge that carries electrons, which collide with atoms in the wire - the longer the wire, the more collisions between electrons+ atoms so increased resistance
describe how the national grid works
- voltage from a generator in a power station is transported to a step-up transformer
- the transformer increases voltage (from around 25,000V-700,000V) so the current decreases - less current means less waste energy is lost as heat
- transmission cables carry high voltage electrical power - above ground to keep people safe from electric shocks
- a step-down transformer reduce voltage to 230V for safe use in homes/industry
