electric circuits Flashcards
what happens when you rub 2 objects together?
become electrically charged as electrons (negatively charged) are transferred to 1 object to another:
- objects receiving electrons negatively
- objects giving up electrons positively
electrical charge = static electricity
what happens when 2 charged materials are brought together?
exert force on each other
- 2 materials with the same type of charge repel
- 2 materials with diff charges attract
eg:
- positively charged perspex rod another pc rod, rod will repel
- negatively charged ebonite rod near to positively charged Perspex rod, will attract
what is an electric current?
flow of charge, measured in amps
what happens in a electric circuit?
- components + wires full of charges that are free to move
- battery causes free charges to move
- charges aren’t used up but flow in a loop
what happens in metal conductors and insulators?
metal conductors:
- lots of charges free to move
insulators:
- no charges free to move
metals contain free electrons in structure which move to create an electric current
what is a direct current?
always flows in same direction
what is an alternating current?
changes direction of flow back and forth continuously
why is alternating used for mains supply instead of current?
- easier to generate
- distributed efficiently
- used in a transformer
what is potential difference?
voltage:
- pd between 2 points in the circuit is the work done on a given amount of charge as it moves between these points
- measured in volts using voltmeter connected in parallel across a component
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greater pd, greater current
more batteries in a series, pd increases
what happens if you add more batteries in parallel?
- total pd + current remain same
- each battery supplies less current
what do components do?
resist flow of charge through them
examples:
- resistors
- lamps
- motors
explain resistance?
greater resistance, smaller the current
if you add another cell in a circuit, what does it provide?
- greater pd
- greater current
what happens if you add resistors in series + parallel?
series:
- batt push charges through more resistors so resistance increases
parallel:
- more paths for charges to flow along so resistance reduces
what happens when a current flows through a component?
causes component to heat up, heating effect large enough to make lamp filament glow
what happens as the current flows?
- moving charges collide with vibrating ions in wire, giving energy
- inc in energy causes component to heat
how can you calculate resistance?
resistance = voltage / current
explain current-voltage graphs?
as components resistance stays constant, current through resistor is directly proportional to voltage across resistor
means graph showing current + voltage in component will be a straight line through 0
what does the thermistor depend on?
temp
as temp increases:
- resistance decreases
- more current flows
what does the LDR depend on?
light intensity
as light intensity increases:
- resistance increases
- more current flows
what are the uses of some electric motors?
hard disk drive - rotate @ high speed
dvd player - rotate so info read
washing mach - rotate drum + agitate wash
tumble dryer - rotate drum + provide uniform heat
microwave - rotate food so evenly heated
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when electric charge flows through device, work is done by power supply
energy is transferred from power supply to device and surroundings
what is power?
- measured in watts
- measure of rate of energy transfer to device and surroundings
how can you calculate power?
power = voltage x current
what are transformers?
used to change voltage of alternating current consisting of 2 coils of wire wrapped around a soft iron core
when 2 coils of wire are close to each other, a changing magnetic field in one coil caused by changes in current can induce a voltage in the other how?
- alternating current flowing through pc creates alternating magnetic field
- changing field induces an alternating current in the secondary coil
what is the equation of the transformer?
amount of which transformer changes voltage depends on number of turns on coils
changing current causes changing magnetic field in iron core which causes a changing pd acriss sc
equation:
v on primary/v on secondary = # of turns on primaru/# of turns on secondary
what is an electric motor?
consists of coil of wire that rites in between opposite poles of a permanent magnet when a current flows through the coil
what can a coil do?
- exert force on magnet or another current carrying wire
- exp a force if placed in a magnetic field whos lines of force are at right angles to the wire. force will be at right angle to both current direction and lines of force of magnetic field. if parallel to magnetic field lines, doesn’t experience force
what happens when a current flows through the coil?
cut field lines in opposite directions on each side of coil creating pair of forces in opposite directions and causing coil to rotate
what is a commutator?
rotary switch that turns with coil but brushes that touch it remain fixed
this has effect of making sure that as coil rotates, has current direction into the coil is switched
when does the current always cut the field lines?
- nearest south pole of magnetic in same direction
- nearest north pole in opposite direction producing pair of opposing forces whose directions remain same
what is mains electricity produced by?
generators that use principal of electromagnetic induction to generate electricity by rotating a magnetic inside a coil
what can the size of voltage be increased by?
- inc speed of rotation of magnet
- inc strength of magnetic field by using electromagnet
- inc # of turns on coil
- placing iron core inside coil
what happens as the magnetic rotates?
voltage induced in coil changes direction and size
current is alternating current as it reverses its direction of flow every half turn of the magnetic, the direction of voltage + current in same direction
what is the electromagnetic induction?
when you move a magnetic into coil of wire, voltage is induced between ends of wire bc magnetic field is being cut
if ends of coil are connected to make a complete circuit, a current will be induced
how can you induce a current in the opposite direction?
- moving magnet out of coil
- moving pole of magnet into coil
no movement of coil or magnet, no induced current
what happens when 2 components are connected in series to a battery?
- current flowing through each component is same = A1 = A2 = A3
- pd across components adds up to pd across battery = V1 = V2 + V3
- pd is largest across components with the greatest resistance
