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Physics > P2 topic 2 > Flashcards

P2 topic 2 Flashcards

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1
Q

when is the heat in resistors made of use?

A

in electric cheaters and the heating element of an electric kettle

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2
Q

what can cause fires?

A

excessive heat produced in electrical devices can cause fires if there are no safety features- an overloaded mains socket is a potential fire hazard

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3
Q

what is an example of safety feature to prevent fires in an electrical device?

A

cooling fan in a laptop

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4
Q

what can be used to calculate how much it would cost to use a device?

A

electrical power

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5
Q

what can be used to calculate how much electrical energy a device will transfer?

A

electrical energy

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6
Q

electrical power

A

the rate of energy transfer

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7
Q

what happens when current flows?

A

electrons travel through the lattice of the metal

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8
Q

what causes heating in a circuit?

A

electric current- the heating is the result of collisions between electrons and the ions in the lattice

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9
Q

heat energy

A

collisions cause increased vibrations (around fixed positions) of the ions

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10
Q

what does LDR stand for

A

light dependent resistor

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11
Q

LDR

A

a special type of resistor made from a semiconductor material

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12
Q

what happens the the resistance of a LDR as intensity of light incident on it increases?

A

the resistance decreases as light intensity increases- more light means less resistance- circuits with LDRs can be used to detect changes in light intensity

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13
Q

thermistor

A

special type of resistor- its resistance depends on temperature- a sensor in a electric circuit that detects temperature changes

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14
Q

what happens to the resistance of a thermistor as temperature increases?

A

the resistance of a thermistor decreases as its temperature increases- greater temperature means less resistance

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15
Q

where are LDRs used?

A

simple light-meters, light-sensitive circuits in burglar alarms and circuits for automatically controlling how much light enters a camera

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16
Q

where are thermistors used?

A

simple electrical thermometer, circuit to switch off fan inside laptop when it overheats, central-heating controller that senses temperature

17
Q

why are metals not used for thermistors?

A

increasing the temperature of a metal does not significantly change the number of conduction electrons- in semiconductors and metal oxides, more temp frees up more electrons from atoms and causes resistance to decrease

18
Q

what are LDRs made from?

A

semiconductors that are responsive to light- as the intensity of light falling on a LDR increases, this frees up more electrons from the atoms and this causes the resistance to decrease

19
Q

what causes a resistor to heat up?

A

the current in the resistor

20
Q

what can be used to determine the resistance in a wire?

A

the potential difference across the wire and the current in the wire

21
Q

what is the relationship between the resistance of a wire and it’s length?

A

the resistance of the wire is directly proportional to its length- the resistance doubles when the the length is doubled

22
Q

rheostat

A

variable resistor

23
Q

how can the resistance of a rheostat be changed?

A

manually

24
Q

what happens when a resistor is set to its maximum value?

A

the current in the circuit is low

25
Q

what is often the lowest value of a resistor?

A

zero

26
Q

what can circuits be used to investigate?

A

how a current varies with potential difference for devices such as a filament lamp, a diode and a fixed resistor

27
Q

filament lamp

A

the current increases with potential difference- as the current increases, the filament gets hotter and the resistance increases

28
Q

fixed resistor

A

the current is directly proportional to the potential difference- its resistance is constant

29
Q

diode

A

only conducts in one direction- it has an infinite resistance when the current is zero- the diode has low resistance when it conducts

30
Q

practical application of a diode

A

a diode only conducts in one direction, when its abode is connected to a positive terminal and its cathode is connected to a negative terminal- a diode and a lamp can be used to work out the polarities of an unmarked cell or power supply

Physics (15 decks)

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