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PHYSICS > Electricity > Flashcards

Electricity Flashcards

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1
Q

Current

A

The rate of flow of charge

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2
Q

What is the unit for current?

A

Ampere (A)

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3
Q

Voltage

A

The driving force that pushes the current round

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4
Q

What is the unit for voltage?

A

Volt (v)

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5
Q

1 volt means…

A

1 joule per coulomb

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6
Q

Resistance

A

Anything in the circuit which slows the flow down

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7
Q

If you increase the voltage…

A

More current will flow

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8
Q

If you increase the resistance…

A

Less current will flow

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9
Q

What does an ammeter measure?

A

The current (in amps)flowing through the component

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10
Q

Where does a voltmeter have to be placed?

A

In parallel around the component under test

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11
Q

What current is mains supply?

A

A.C (alternating current)

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12
Q

What current is Battery supply?

A

D.C (direct current)

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13
Q

What does a voltmeter measure?

A

The voltage (volts) across the component

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14
Q

What are the wires in plugs?

A

live wire
neutral wire
earth wire

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15
Q

Colors of wires in plug:

A

live wire is brown
neutral wire is blue
earth wire is yellow and green

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16
Q

What does the live wire alternate between?

A

high +VE and -VE voltage of about 230 V

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17
Q

What voltage is the neutral wire?

A

0V

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18
Q

Why must appliances with metal cases be ‘earthed’?

A

To reduce the danger of an electric shock

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19
Q

What is double insulation?

A

When an appliance has a plastic casing

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20
Q

Do appliances with double insulation need an earth wire?

A

NO

21
Q

What safety precautions should you take when using plugs?

A

check case isn’t missing, cracked or broken
check cable isn’t frayed
check cables aren’t too long
check theres no water near

22
Q

Earthing and fusing prevents..?

A

Fires and shocks

23
Q

What happens if a fault develops in which the live wire touches the metal case?

A

a big current flows through the live, through the case, and down the earth wire
this surge in current blows the fuse, which cuts off the live supply

24
Q

What are the advantages circuit breakers have over fuses?

A

They can easily be reset

25
Q

What is another type of circuit breaker?

A

A RCCB

26
Q

Electrical Power=

A

Current x Voltage

27
Q

When a charge drops through voltage what happens?

A

energy is transferred

28
Q

What is voltage?

A

the energy transferred per unit charge passed

29
Q

What is a volt?

A

one joule per coulomb

30
Q

What happens when two insulating materials are rubbed together?

A

electrons will leave one material and be attracted to the other, leaving a positive charge on one material and a negative charge on the other

31
Q

what is a build up of static caused by?

A

friction

32
Q

Describe what would happen when a polythene rod is rubbed with a cloth duster in comparison with when an acetate rod is rubbed with it

A

Polythene rod + cloth duster: electrons move from the duster to the rod. The rod becomes negatively charged and the duster is left with an equal positive charge
acetate rod + cloth duster: electrons move from the rod to the duster. The duster becomes negatively charged and the rod is left with an equal positive charge

33
Q

What are positive electrostatic charges caused by?

A

Electrons (negatively charged) moving elsewhere - the loss of electrons

34
Q

What are negative electrostatic charges caused by?

A

The gain of electrons

35
Q

How can a charged conductor be discharged safely?

A

By connecting it to earth with a metal strap. The electrons flow down the strap to the ground if the charge is negative and flow up the strap from the ground if the charge is positive

36
Q

What is electric current?

A

The rate of flow of electrical charge

37
Q

what happens if there is a large voltage on an isolated object?

A

a spark jumps across the gap between it and earth

38
Q

Like charges…

A

repel

39
Q

Opposite charges…

A

attract

40
Q

Describe an experiment to demonstrate whether a material is charged using a gold-leaf electroscope

A
  1. A gold-leaf electroscope has a metal disc connected to a metal rod, at the bottom of which are attached two think pieces of gold leaf
  2. When a rod with a known charge is brought near to the disc of the electroscope, electrons will either be attracted to or repelled from the metal disc depending on the charge of the rod
  3. This induces a charge in the metal disc, which in turn induces a charge in the gold leaves
  4. Both the gold leaves will have the same charge, so they will repel each other causing them to rise
  5. When the rod is taken away the gold leaves will discharge and fall again
41
Q

Describe how to test whether a rod of material is charged

A
  1. suspend a rod with a known charge on a thread and see if there is repulsion or attraction when the rod you’re testing is brought close to it
  2. if there is an attraction, the test rod has the opposite charge to the suspended rod. If there is repulsion, then the test rod has the same charge as the suspended rod
42
Q

what is a Van de Graaff generator used for?

A

to demonstrate electrostatic charges

43
Q

What is a Van de Graaff generator made up of?

A

a rubber belt moving around plastic rollers beneath a metal dome

44
Q

What will happen if you stand on an insulated chair and put your hands on the dome of a Van de Graaf generator?

A

electrons will move between your body and the dome, giving your body a charge. The human body conducts charge, and like charges repel, so the charges will spread out as much as possible throughout your body. The charge is strong enough to make your hairs repel each other and stand on end

45
Q

How is static electricity used in an inkjet printer?

A
  1. tiny drops of ink are forced out of a fine nozzle, making them electrically charged.
  2. the droplets are deflected as they pass between two metal plates. A voltage is applied to the plates: one is positive, the other negative
  3. the droplets are attracted to the plate of the opposite charge and repelled from the plate with the same charge
  4. the size and direction of the voltage across each plate changes so each droplet is deflected to hit a different place on the paper, making up the printout
46
Q

How is static electricity used in a photocopier?

A
  1. The image plate is positively charged. An image of what you’re copying is projected onto it
  2. Whiter bits of what you’re copying make light fall on the plate and the charge leaks away in those places
  3. The charged bits attract negatively charges black powder which is transferred onto positively charged paper
  4. The paper is heated so the powder sticks
47
Q

How is lightning caused by static electricity?

A

Rain drops and ice bump together inside storm clouds, knocking off electrons and leaving the top of the cloud positively charged and the bottom of the cloud negatively charged. This creates a huge voltage and a big spark

48
Q

What is the danger caused by static charge whilst filling a car with fuel? What is the solution to this problem?

A

As fuel flows out of a filler pipe, static can build up. This can easily lead to a spark and in dusty or fume places an explosion or fire.
Solution: make the nozzles out of metal so that the charge is conducted away instead of building up. It’s also good to have earthing straps between the fuel tank and the fuel pipe.

PHYSICS (8 decks)

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