# P5- Electric circuits

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• Created by: Naana
• Created on: 30-05-14 17:08
What causes the build up of static electricity?
Friction. When two insulating materials are rubbed together, electrons are scraped off one and dumped on another. Electrons- ve charged so this leaves a positively static charge on one (electrons scrapped off) and negative charge on other (gained ele
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When electrons are removed from particles what type of particle is left?
Positively charged particles called ions
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Do positively charged particles move?
No they don’t move. A positive static charge is always caused by electrons moving away elsewhere
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Describe the forces between objects with like charges and opposite charges
Two objects with like charges repel each other, whereas two objects with opposite charges attract each other.
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What is an electric current?
This is a flow of charge round a circuit
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Explain why metals are good conductors of electricity
Because metal conductors are full of charges (electrons) that are free to move around and so electrical charges can flow.
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Explain what current, voltage and resistance are in an electric circuit
A current (A) will only flow through a component if there is a voltage. Voltage (V) is the driving force that pushes the current round. Resistance (R) is caused by things in the circuit e.g.lamps that resist the flow of charge (slows the charge down
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What happens to the current if you increase the voltage?
If you increase the voltage, then more current will flow
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What happens to the current if you increase the resistance?
If you increase the resistance, then less current will flow
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Define power
Power in the rate at which an electrical power supply transfers energy to an appliance
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What does an appliance with a high power rating do?
It transfers a lot of energy in a short time. This energy comes from the large current flowing through it.
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What is another name for voltage and what is it a measure of?
Potential difference. This tells us how much energy is transferred to or from each unit of charge as it moves between two points. It also measures the work done on or by a charge as it passes between two points.
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What do voltage current graphs show?
It shows how the current in a circuit varies as you change the voltage
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What does the slope of a voltage current show?
It shows resistance. The steeper the slope the lower the resistance
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What causes resistors to increase in temperature?
When electrons move through a resistor they collide with positive ions, which cause the ions to vibrate more and this results in the resistor getting hotter.
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What is a LDR and how does the resistance vary with light intensity?
A light dependant resistor is a special type of resistor that changes its resistance depending on how much light there is. In bright light, the resistance falls and in darkness the resistance is highest.
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What is a thermistor?
It is a temperature dependant resistor. In hot condition the temperature drops, whereas in cool conditions, the resistance goes up.
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Explain why potential difference is shared out in series circuit
This is because the total work done (energy transferred) on the charge by the battery must equal the total work done by the charge on the components.
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Why is the current the same everywhere in a series circuit?
Because the same current flows through all parts of the circuit
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In a parallel circuit, why is the potential difference the same across all components? What does this mean for identical bulbs?
Because in parallel circuits, the P.D. across each component is equal to the P.D of the battery. This means that identical bulbs connected in parallel will be at the same brightness.
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In a parallel circuit, what happens to the current flowing from a battery?
The current flowing from the battery is shared between the branches. So the total current leaving the battery is equal to the total of the currents in the separate branches.
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What does the current that is pushed through a component depend on?
It depends on the resistance. The resistance of a component controls how much current is able to push through it. The component with the least resistance has the largest current.
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What voltage are UK mains electricity supplied at? And why is AC used?
230 V. Alternating current is used, which is a current which constantly changes direction because it is easier to generate than DC and easier and simpler to distribute over longer distances.
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Define electromagnetic induction
This is when you can create a voltage and then a current in a conductor by moving a magnet in or near a coil of wire.
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Explain how a generator works
In a generator, a magnet rotates in a coil of wire. As the magnet turns, the magnetic field through the coil changes-this change in the magnetic field creates a voltage, which makes a current flow in the coil.
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What are the four factors that affect the size of the induced voltage produced by a generator?
The presence of an iron core inside the coil, the strength of the magnetic field, the speed of rotation and the number of turns on the coil.
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What are transformers used for?
Used to change size of the AC voltage-use electromagnetic induction. They have two coils of wire, primary and secondary coils. Step up- increase the voltage-have more turns on secondary coil. Step down- decrease voltage- more turns on primary coil.
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Define magnetic field
A magnetic field is a region where magnetic materials like iron and steel and also wires carrying currents experience a force acting on them
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What part of an electric motor reverses the direction of the current? Why is this important?
Split ring commutator reverses the current direction every half turn to keep the coil rotating continuously in same direction. It stops the direction of the force reversing every 1/2 turn, coil changing direction every1/2 turn inst of rotating fully
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Name 3 items that use electric motors
DVD players, electric cars and domestic appliances (washing machines)
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## Other cards in this set

### Card 2

#### Front

When electrons are removed from particles what type of particle is left?

#### Back

Positively charged particles called ions

### Card 3

#### Front

Do positively charged particles move?

### Card 4

#### Front

Describe the forces between objects with like charges and opposite charges

### Card 5

#### Front

What is an electric current?