# P2 Unit 2: Controlling and using electric

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• Created by: nicola
• Created on: 25-05-15 09:46
What is an Ammeter?
An ammeter measures the amount of current passing through it in (A) Amps therefore it must be placed in seris (before or after) with the component so it can measure the amount of current travelling through it.
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What are Junctions?
Current is conserved at a juncation. the amount of curent going into the juncation will always be the same as the amount of current leaving the junction.
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How do you make a current?
A current flows around a circuit when it is 'pushed' by a Potential difference P.D (voltage) provided by a cell, battery or a power pack. The bigger the Potential difference (for the same circuit) the bigger the curent.
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What is a Voltmeter?
Voltmeter measure the amopunt of potential difference across a component (the difference from one side to the other) in volts therefore it must be attached parallel (across) to the component.
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What is a volt?
A volt is the amoiunt of energy measured in Joules (J) carried by each Coulomb of charge.
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What is a Resistant?
The reesistant of a circuit or component is a measure of how difficult it is to get the curren t to flow the greatest the resistant the less the current (for the same voltage).
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What is a variable resistor? 1/2
Variable resistor enables you to change the resistant in a circuit and therefore the amount of current flowing in the circuit.
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What is a variable resistor? 2/2
(Set the variable resistant to a high resistance the current will be low, se the variable resistor to a low resistance the current will be high).
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What is a fixed resistor?
Fixed resistors always have the same step up in voltage always produces the same step up in the current. (the current is proportional to the voltage).
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What are filament lamps? How do filament lamps work? 1/2
The thin metal wire inside a filament lamp gets hot when current flow through it i.e. the metal ions in the wire vibrate more and get in the way of the flow of electrons thus increasing the resistance in the wire.
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What are filament lamps. How do filament lamps work? 2/2
The hotter the wire the greater the resistances so bigger step up in voltage are needed to get the same step up in current at higher currents, which neats the wire than lower current.
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What is a Diodeas? How do Diodes work?
Diodes only let the current flow in one direction. if the potential difference is reversed (by turning round the battery) no current is allowed to flow. (They have nearly zero resistance in one direction but a huge resistance in the other direction).
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What are Light Dependent Resistors (LDRs)? How do LDRs work? 1/2
A LDR's resistance changes when the intensity of light falling on it charnges. The greater the intensity of light falling on the LDR the smaller the resistance, the smaller the intensity of light falling on the LDR the greater the resistance.
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What are Light Dependent Resistors (LDRs)? How do LDRs work? 2/2
Dark = High resistant. Light = low resistant. LDR are used in camera and street lights that turn themselves on when it gets dark.
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What are Thermistor? How do Thermistor work?
A thermistor's resistance changes with its temperature. the greater the temperature the smaller the resistance of the thermistor, the smaller the temperature the greater the resistance of the thermistor. Cold = high resistance. Hot = low resistance.
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What are thermistors used for?
Thermistors are used to control hot water tanks and are used in thermostats.
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How do wire/resistor heat up? Why do wire/resistors heat up? 1/2
A wire/resitor gets hot when a current flows through it because the electrons collide with the ions in the wire/resistor.
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How do wire/resistor heat up? Why do wire/resistors heat up? 2/2
The kinetic (movement) energy the electrons have is transferred to the ions in lattice of the wire/resistor during the collision which causes the wire to heat up/gain energy in the form of heat.
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What are the uses of heating a wire or resistor?
The heating effect of current can be an advantage such as in electric blankets or hairdryers where heat is required. A disadvantage is other applances like computers and lights where the heat energy is wasted or cause the appliance to overheat.
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## Other cards in this set

### Card 2

#### Front

What are Junctions?

#### Back

Current is conserved at a juncation. the amount of curent going into the juncation will always be the same as the amount of current leaving the junction.

### Card 3

#### Front

How do you make a current?

### Card 4

#### Front

What is a Voltmeter?

What is a volt?