Electricty Flashcards
The equation for charge Q =
Q = IT
Current is the ….
flow of charge per second
What is an electrical conductor and give examples?
a material that current flows well in
eg metals, graphite (as they have delocalised electrons)
What is an electrical insulator and give examples?
a material that current does not flow well in
eg plastic, rubber,
Describe what happens when we charge by friction.
eg polythene rubbed with cloth rub cloth on polythene electrons gain energy and move from cloth to rod rod becomes negatively charged cloth becomes positively charged
Why can we only charge insulators and not conductors?
Conductors cannot be charged as they can conduct so would carry the charge away
Laws of electrostatic forces?
Like charges repel
Unlike charges attract
Dangers of electrostatics?
Refueling aircraft and tankers
Charge can build up and all jump at once in the form of a spark. This can ignite the fuel causing a fire.
Earthing metal stops charge building up.
Uses of electrostatics?
Photocopiers
Inkjet printers
Paper is charged with one charge and the ink charged with the opposite charge.
Unlike charges attract so ink is attracted to the paper
Smoke precipitators
charge smoke particles in chimney
charge plates each side with opposite charge
unlike charges attract so smoke sticks to plates and is removed before the gas enter the air
Equation for current I
I = Q/t
Q= It
Equation for voltage
Voltage = energy/ charge
V = E/Q
= joules per coulomb
Equation for resistance
V = IR
Current in series is……
The same everywhere
Voltage in series….
Voltage splits
Bigger resistance takes bigger voltage
Current in parallel…..
Splits at junctions between branches
Voltage in parallel…..
Same across each branch
Power =
Power = IV
Power lost to heat in a circuit =
P = IxIxR
List 4 things that protect a device or user in electrical circuits.
Double insulation
Earthing
Fuses
Circuit breakers
Energy transferred =
Energy transferred = IVt
What’s the difference between ac and dc current?
AC is alternating and changes direction 50 times per second
DC is direct and flows in one direction only
AC in mains
DC in batteries
For wires and resistors, as temperature increases then resistance ….
Increases
Particles have more KE so electrons collide more with the lattice ions
Conventional current flows positive to negative but in a metal conductor electrons in the wire flow…
Negative to positive
What can we use in a circuit to indicate the presence of current?
an LED
What resistance does an LDR have in the light?
light gives low Resistance
What resistance does a thermistor have when hot?
hot gives low Resistance
Are series or parallel circuits best for domestic lighting? Why?
parallel
each light can be controlled separately by own switch
if one buld blows, others still work
Why are some Christams lights wired in series?
less wires
cheaper
voltage shared between bulbs
