OCR 21st Century Science P5

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What causes a build up of static?
Friction from two insulating materials.
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What is static electricity?
Charges which are not free to move.
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Give 3 examples of Static Electricity
Static electricity attracts dust, causes clinging clothes and hair to stick up.
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What is electric current?
The flow of charge through of circuit
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What do the wires in a circuit contain?
They are full of electrons that can be moved with voltage.
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What is voltage?
The driving force that pushes current around.
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What is resistance?
Components that resist the flow of charge and slow it down.
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What is power?
Power is the rate of energy transfer and is voltage * current.
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What does a voltmeter measure?
The potential difference between two points and how much energy is transferred two or from each unit of charge as it moves between two points.
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What does the slope of a volt-current graph show?
Resistance
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What is Ohm's law?
The law that states that current through a component is directly proportional to voltage across it when resistance stays constant.
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What is the formula for resistance?
Resistance = voltage / current
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Why do resistors get hot when current passes through them?
Because the electrons collide with the resistor's positive ions and causes vibrations and thus heat energy is generated.
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What is a LDR?
An LDR is a resistor that changes it's resistance depending on light. In bright light resistance falls and in darkness resistance increases.
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What is a thermistor?
A thermistor is a resistor where the resistance depends on temperature. In hot conditions the resistance drops while in cooler conditions the resistance goes up.
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What is the formula for potential difference in a series circuit?
Supply voltage = V1+V2...
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What is the formula for current in a series circuit?
It is the same everywhere in the circuit, A1 = A2 = A3
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What is the formula for resistance in a series circuit?
In series circuits the total resistance is the sum of all individual resistances. R= R1 + R2 + R3
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How do total cell voltages work?
Cell voltages connected in series add up while cell voltages connected in parallel don't add up.
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How do cell currents work?
In series circuits each cell current is the same as that circuit's total current whilst in parallel circuits the current of cells adds up.
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What is the formula for P.D in a parallel circuit?
P.D is the same across all components, V1 = V2 = V3
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What is the formula for current in a parallel circuit?
Total current is the sum of the current of the individual branches, A = A1 + A2
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What is the formula for resistance in a parallel circuit?
1/Rt = 1/R1+1/R2...
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What is the difference between mains supply and battery supply?
Mains supply is AC while battery supply is DC.
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What is the difference between AC and DC?
AC is when the current is constantly changing direction while DC current always flows in the same direction.
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How can you create a voltage?
By moving a magnet in or near a coil of wire, the process is called electromagnetic induction.
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How does electromagnetic induction work?
As you move the magnet through the coil, the magnetic field changes and this change in magnetic field induces a voltage in the coil.
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How do AC generators work?
By a magnet rotating in a coil of wire and as the magnet turns, the field through the coil changes which induces a voltage and makes a current flow through the coil.
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How is an ALTERNATING current generated?
As the magnet is turned through half a turn the direction of the magnetic field through the coil reverses so the current flows in the opposite direction.
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How could you increase the voltage induced?
You could add an iron core inside the coil, increase the strength of the magnetic field, increase rotation speed and increase turns on coil.
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What is the function of a transformer?
To change the size of a voltage.
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What do transformers consist of?
They consist of an iron core with a primary coil of wire and secondary coil of wire wrapped around it.
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How do transformers work?
The AC current flowing in the primary coil causes changes in the iron core's magnetic field which induces a changing voltage in the secondary coil.
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What does a step up transformer do?
Step up transformers increase the voltage by having more turns on the secondary coil.
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What does a step down transformer do?
Step down transformers decrease the voltage by having more turns on the primary coil.
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How do transformers work by electromagnetic induction?
The primary coil produces a magnetic field in the iron core and because of the AC in the primary coil the magnetic field in the iron core constantly changes direction which induces an alternating voltage in the secondary coil.
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What is the transformer equation?
Vp/Vs = Np/Ns
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What is a magnetic field?
A magnetic field is a region where magnetic materials and also wires carrying currents experience a force acting on them.
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What is created by a current carrying wire?
A magnetic field.
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What does a rectangular coil do?
A rectangular coil the circular magnetic fields around the sides of the loop reinforce each other at the centre. More turns a more reinforced field.
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What is Fleming's left hand rule?
The rule where your thumb represents force, your first finger the field and your second finger the current.
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What is the motor effect?
The motor effect is when a wire carrying a current is placed in a field and the force causes it to turn.
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What is a split ring commutator?
A split ring commutator is a device which swaps the contacts every half turn.
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What is the split ring commutator for?
The split ring commutator keeps reversing the direction of the current every half turn to keep the coil rotating continuously in the same direction otherwise the coil would never fully rotate.
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Give examples of electric motor usage.
A disc spinner, electric vehicle wheels and domestic appliances.
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Other cards in this set

Card 2

Front

What is static electricity?

Back

Charges which are not free to move.

Card 3

Front

Give 3 examples of Static Electricity

Back

Preview of the front of card 3

Card 4

Front

What is electric current?

Back

Preview of the front of card 4

Card 5

Front

What do the wires in a circuit contain?

Back

Preview of the front of card 5
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