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13095642
Electricity
Descripción
GSCE Physics Mapa Mental sobre Electricity, creado por h g el 03/04/2018.
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phy
physics
gsce
Mapa Mental por
h g
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h g
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Resumen del Recurso
Electricity
Current, potential difference and resistance
Circuit symbols
Current and charge
cell/battery provides a potential difference
which gives a current
p.d. = voltage(Volts)
current is carried by electrons which are free to move
direction in which positive charge would flow
measured in ampere(A)
charge(Q) is measured in coulombs(C)
1C = 6 billion billion electrons
Q = It
Controlling the current
change in size of p.d. will change the size of the current (increase=increase)
increasing resistance will decrease the current
Ammeters and voltmeters
ammeter is set up in series with the resistor
voltmeter is placed in parallel with the resistor
the voltmeter only allows a very small current to flow through it, so it doesn't affect the current
Resistance
depends on two things
1. resistance of component
2. p.d. across the component
V = IR
measured in ohms
Current-potential difference characteristics graph
An ohmic conductor
at constant temperature; current and p.d. is proportional
straight line through the oigin
resistor = ohmic
A filament lamp
line curves away from y-axis
resistor = non-ohmic
increase in current = increase in resistance
current inc. = temperature inc.
A diode
current only allowed to go in one direction
current starts when p.d. = 0.7V
example: LED
reversed p.d. = no current
Changing resistance
by reacting to surroundings
i.e. thermistor (temperature)
temp. inc. = resistance. dec.
fire alarm
LDR
bright light = low resistance
dark light = high resistance
Series and parallel circuits
Series circuits
same current through each component
total p.d. of the power supply is shared between the components
V(supply) = V1 + V2
total resistance of two components is the sum of each coponent
R(total) = R1 + R2
Parallel circuits
p.d. across each component is the same
total current = sum of currents through separate components
total resistance of two resistors in parallel is less than the resistance of the smaller individual resistor
Cells and batteries
battery = two or more electrical cells
total p.d. is calculated by adding separate p.d.s together(only works if the cells are joined facing the same way(+ to -))
Circuit calculations
use circuit rules to solve circuit problems
Domestic use and safety
Direct and alternating potential difference
direct p.d. = direct current(d.c.)
current and p.d. flows in one direction
alternating p.d. = alternating current(a.c.)
current and p.d. switches direction many times er second
Mains supply
supplied by a.c.
UK: p.d. of 230V and frequency of 50Hz
Cables
connect to a wall-socket using a three-core cable plug
cross-sectional area of 2.5mm^2
no more than 13A
larger appliances = thicker cables
Live, neutral and earth wires
live
alternating p.d. from the mains supply
230V
neutral
completes the circuit
carry current to and from the electrical appliance
very close to 0V
earth
stops appliance from becoming live
0V
Earthing
joining earth wire from three-core cable plug to metal casing of appliance
Power
Energy and charge
charge passing through a resistor: resistor gets hot
electrons passing through collide with atoms of the resistor
amount of energy depends on two things
p.d. across the resistor
how much charge flowing through
E = VQ
Power and energy
energy transferred depends on two things
power of appliance
how long it's switched on
E = Pt
since I = Q/t
P = VI
since V = IR
P = I^2 R
National grid
1. power station sends 1000A and 25000V
2. transformer transforms to 400 000V and 62.5A
3. transformer transforms to 230V and larger current (for us to use in our homes)
Static electricity
Making static
Sparks
the more teo insulating objects are rubbed against each other, the more charge is built up - can lead to a spark
lightning
walking on a carpet
Energy transfers in lightning
1. thunder cloud is charged: energy is stored in an electrostatic store
2. cloud discharges: work is done when charge flows to the earth
3. energy is transferred to the surroundings by heating, radiation and sound
4. energy carried by sound and light is transferred to the thermal stores of the surroundings
Forces on charges
pos and pos // neg and neg repells
pos and neg attracts
rubbing insulating materials together
neg. charged particles are rubbed off one and onto the other
when combing hair with a nylon comb: comb becomes neg. charged
when rubbing a perspex ruler with a duster: duster becomes neg. charged
Electric fields
gravitational
magnetic
electric
charged object creates this around itself
strongest closest to the object
direction of field is that of the force of a positive charge
strength is increased by adding more charge to object
Recursos multimedia adjuntos
Cell (binary/octet-stream)
Battery (binary/octet-stream)
Switch (binary/octet-stream)
Closed Switch (binary/octet-stream)
Lamp (binary/octet-stream)
Fixed Resistor (binary/octet-stream)
Ammeter (binary/octet-stream)
Voltmeter (binary/octet-stream)
Variable Resistor (binary/octet-stream)
Fuse (binary/octet-stream)
Diode (binary/octet-stream)
Light Emitting Diode (Led) (binary/octet-stream)
Light Dependent Resistor (Ldr) (binary/octet-stream)
Thermistor (binary/octet-stream)
A.C. And D.C. Graph (binary/octet-stream)
National Grid Diagram (binary/octet-stream)
Electric Field Diagram (binary/octet-stream)
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