CP9

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Explain electron flow.
All metals have electrons that are in the outer shell and only weakly attracted to the nucleus. These electrons can be easily removed, so a metal wire has many 'free' electrons. When a battery is attached, the voltage pushes the electrons
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Why do the electrons move towards the battery?
The electrons are negatively charged so they are attracted to the positive terminal of the battery
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What is conventional current?
Conventional current direction goes from the positive terminal to negative terminal of the battery
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What are circuit diagrams used for?
To show the components and junctions in a circuit
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Components in circuits can be connected in...
series or parallel
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Explain a series circuit.
In series, there is only one route the current can take around the circuit.
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Explain a parallel circuit.
In parallel, there are junctions that allow the current to take different routes
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What happens to lamps in a series circuit? How is this different to parallel?
The lamps cannot be switched on or off individually, and if one fails they all turn off. In parallel, lamps can be switched on/off individually
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What is current measured in? What is it measure with?
Amperes/Amps- with an ammeter
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What does it mean by 'current is conserved'?
The total amount of current stays the same on its journey around the circuit, the current leaving the battery's positive terminal is the same as the current arriving at the negative terminal
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Explain current conservation in parallel.
The current splits at junctions to travel along different branches, but the total amount entering the junction is the same as the amount leaving
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What does potential difference do in a circuit?
it pushes the current around an electric circuit
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For current to flow;...
the circuit must be closed and contain a source of potential difference like a cell or battery
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The bigger the potential difference across a component...
the bigger the current
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Explain potential difference in a parallel circuit.
In parallel, the potential difference across each branch is the same. When there is more than one component in a branch, the potential differences across all components add up to give the total potential difference supplied by the cell/battery
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What is potential difference measured in? What is it measure with?
Volts- using a voltmeter
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What is electric charge measured in?
Coulombs (C)
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What is electric current?
Electric current is formed by moving charged particles. Its the rate of flow of charge.
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What is the equation for charge?
charge=current x time
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What can the equation for charge be written as?
Q=l x t
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The current in a lamp is 0.6A. How much charge flows through it in 1 minute?
0.6A x 60s=36C
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Explain potential energy.
A cell contains a store of energy. Energy is transferred from the cell to the charge. The charge can then transfer energy to the components in a circuit. It has potential energy.
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What is the equation for energy transferred?
Energy transferred= charge moved x potential difference
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What can the equation for energy transferred be written as?
E=Q x V
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The potential difference across a lamp is 1.5V. When the circuit is switched on, 600J of energy is transferred in the lamp. How much charge flowed through the lamp?
600J/1.5V=400C
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What is resistance measure in?
Ohms
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What is the equation for resistance?
Resistance= Potential difference/current
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What is the equation for potential difference?
potential difference= current x resistance
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What can the equation for potential difference also be written as?
V= L X R
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Calculate the resistance in the circuit when the potential difference is 9V and the current is 0.3A
9V/0.3A=30 Ohms
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What is a resistor?
A resistor is an electrical component that restricts the flow of electric current.
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What is a thermistor?
Thermistors are used as temperature sensors, for example, in fire alarms.
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What is a diode?
Diodes are electronic components which can be used to regulate the potential difference in circuits and to make logic gates.
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What is a filament lamp?
A filament lamp is a common type of light bulb. It contains a thin coil of wire called the filament. This heats up when an electric current passes through it, and produces light as a result.
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What is a LDR?
LDRs (light-dependent resistors) are used to detect light levels, for example, in automatic security lights
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When resistors are connected in series...
The total resistance of the circuit is increased- the pathway becomes harder for current to flow through. The potential difference is shared between the resistors, but it may be not equal- there will be greater PD across resistors with higher resistance
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When resistors are connected in parallel...
The total resistance of the circuit is less than the resistance of the individual resistors-there are now more paths for the current
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What is a variable resistor?
A variable resistor is used to change current
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What is Ohms law?
The current flowing through a resistor at a constant temperature is directly proportional to the potential difference across it.
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What does a negative value of potential difference on the graph mean?
A negative value means that the potential difference is applied in the opposite direction.
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What does the graph for a resistor look like?
A straight line through the origin means current is proportional to potential difference. The resistance is constant.
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Explain the shape of the graph for a filament lamp.
As the potential difference and current increase the filament gets hot. Its resistance increases, so there is a smaller increase in current for each increase in potential difference.
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Describe the shape of the graph for a diode.
As the potential difference increases the resistance drops. Current increases as PD increases.The resistance is very high when the PD is applied in the opposite direction. This means that current can only flow through a diode in one direction
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How is an LDR different to a normal resistor?
The resistance of an LDR decreases as the light intensity falling on it increases.If the light intensity falling on the LDR stays the same, the LDR acts like a normal resistor
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How is a thermistor different to a normal resistor?
The resistance of a thermistor decreases as its temperature increases. If the temperature of a thermistor stays the same, the thermistor acts like a normal resistor.
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"the resistance increases as the temperature increases"
filament lamp
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"the resistance increases as the light intensity decreases"
Light-dependant resistor
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"the resistance increases as the potential difference increases"
filament lamp
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"resistance is very high for potential differences in one direction"
diode
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When a current is passed through a resistor, energy is transferred because...
electrical work is done against the resistance. The energy is then transferred by heating and the resistor becomes warm.
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When is the heating effect useful and not useful?
useful- electric heater/ kettle. Not useful- computer/plugs and wires-means useful energy is being transferred by heating and spread out/dissipated. The surroundings gain thermal energy,
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Explain how a resistor works (structure)
As the free electrons flow through the lattice of vibrating ions, they collide. The more collisions=harder it is for them to pass through- the higher the electrical resistance. When the electrons collide, they transfer energy.
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How can we reduce resistance?
By using wires made from metals with low resistance/ use thicker wires. Can also be decreased by cooling metals so the lattice ions aren't vibrating as much
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What is the equation for energy transferred (in circuits)?
Energy transferred= current x potential difference x time - (E=I X V X T)
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What is the equation for electrical power?
Electrical power= current x potential difference - (P=I X V) OR electrical power= current2 x resistance - (P= L X L X R)
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Appliances that need a lot of power use...
mains electricity
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What is the national grid?
The netw ork of cables and wires that carries electricity to our homes
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What is direct current?
If the current flows in only one direction it is called direct current, or DC.
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What is alternating current?
If the current constantly changes direction it is called alternating current, or AC. Mains electricity is an AC supply. The UK mains supply is about 230 V.
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What is a fuse?
A tube with a thin wire inside- the current passes through and the wire gets hotter. If the current exceeds a certain value, the wires melts which breaks the circuit and stops the current. Safety device.
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How many wires are in a mains electricity cable and what are they?
3- The Live wire, (Brown- held at voltage 230V and provides current) Neutral wire, (Blue- completes circuit) and Earth wire (Green and yellow striped-to stop the appliance becoming live)
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What are the safety features?
Switches, the fuse, Circuit breakers (alternate fuses)
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What do circuit breakers do?
They detect a change in current and safely switch off supply
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What are the advantages and disadvantages of circuit breakers and fuses
Circuit breakers they can be switched on again after a fault, but fuses need to be replaced. Some circuit breakers work very quickly and can save lives while fuses take a while to melt- you still get shocked if for e.g you touch a live wire
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Other cards in this set

Card 2

Front

Why do the electrons move towards the battery?

Back

The electrons are negatively charged so they are attracted to the positive terminal of the battery

Card 3

Front

What is conventional current?

Back

Preview of the front of card 3

Card 4

Front

What are circuit diagrams used for?

Back

Preview of the front of card 4

Card 5

Front

Components in circuits can be connected in...

Back

Preview of the front of card 5
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Elephant132

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This is so useful thanks to whoever made it, it actually helps me understand the content effectively 

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