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Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Ring main circuits consist of 3 types of wires:

A
  • Live wire
  • Neutral wire
  • Earth wire
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2
Q

Advantage of ring main circuits:

A

Reduces the amount of wiring needed

Several applications in different parts of the same room can be connected to the mains with minimum wiring

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3
Q

How does a fuse work?

A

A fuse has a thin wire with a low melting point. So, if a large current passes through it, the wire melts breaking the circuit and stopping the flow of current to the device preventing an electric shock or fire

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4
Q

How does a circuit breaker/ trip switch work?

A

If too large a current passes through it the switch automatically opens breaking the circuit. Once the fault has been corrected, the switch is reset

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5
Q

How does earth wiring prevent an electric shock?

A

It is attached to the metal casing of an appliance so that if there is a break/ damage in the live wire, it provides a low resistance path for the current

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6
Q

Do double insulated appliances need earth wiring?

A

NO

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7
Q

Why should the switch be placed in the live wire?

A

So that when the switch is open, electricity is not passed through the wire to the appliance

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8
Q

How is the heating effect of a current used in appliances?

A

The wires of a heating element have high resistance so current builds up in the wires and energy is transferred and the element heats up

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9
Q

Write the equation relating to power, voltage, and current

A

P = I x V

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10
Q

How to calculate the total energy transferred by an appliance?

A

E = P x T

E = I x V x T

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11
Q

What is an alternating voltage?

A

A voltage that is continuously changing its value and direction

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12
Q

What type of voltage do cells and batteries use?

A

Direct current

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13
Q

What is an electric current?

A

The flow of charge carried by electrons

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14
Q

The direction of flow of charge in a conventional current:

A

From +ve terminal to the -ve terminal

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15
Q

One coulomb is equal to the charge carried by ________ electrons

A

6 x 10¹⁸

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16
Q

Current is measured using ______ in units called ______

A

Ammeter

Amperes (A)

17
Q

What is the relationship between the electric charge, current, and time

A

Q = I x t

18
Q

What is voltage?

A

The amount of energy supplied to each coulomb of charge

19
Q

What does the voltage across a component indicate?

A

It indicates the energy transferred by the component (as a coulomb passes through it)

20
Q

Write the equation for the relationship between energy transferred, charge, and voltage

A

E = Q x V

E = I x t x V

21
Q

Draw circuit symbols for:

a) Diode
b) Variable resistor
c) Thermistor
d) LDR

A

(a) —ⅼ◀—
(b) ↗
(d) ↘↘

22
Q

What are the features of a series circuit?

A
  • One switch placed anywhere in the circuit can turn all the bulbs on and off
  • If any one bulb breaks, causes the circuit to become incomplete and others will also not work
  • The voltage is shared between the bulbs so their brightness reduces if a bulb is added
  • The current is the same throughout the circuit
23
Q

What are the features of a parallel circuit?

A
  • A switch can be placed in different parts of the circuit to turn the bulbs on and off individually or all together
  • If one bulb breaks, only the bulbs on the same circuit will not work
  • The voltage is equal in all the branches so the bulbs’ brightness remains the same if a bulb is added
  • The current is not the same throughout the circuit. The current entering a junction is equal to the current leaving the junction
24
Q

Voltage, current, and resistance are related as follows:

Unit of resistance:

A

V = I x R

Ohms Ὼ

25
Q

What is the function of fixed resistors in a circuit?

A

It controls the sizes of currents and voltages in a circuit

26
Q

What is the function of variable resistors in a circuit?

A

Allow you to alter the resistance

Can be used as a dimmer switch, to control the speed of a motor

27
Q

Where are thermistors used?

A

In fire alarms, freezers, and computers

28
Q

Where are LDRs used?

A

In photographic exposure equipment, automatic lighting controls, and burglar alarms

29
Q

How does a Diode work?

*LEDs

A

A type of resistor that has a low resistance when current is flowing in one direction but a high resistance if the current is flowing through it in another direction

*These diodes light up when charges flow through them

30
Q

Where are diodes used?

A

In rectifier circuits which convert a.c to d.c

31
Q

What should be the electrical conductivity of two objects that gain an electric charge by friction?

A

They should be electrical insulators

32
Q

How does electrostatic spray painting work?

A

The metal nozzle of the spray is going to be +vely charged and so as the pant particles leave, they will repel and form a thin spray.

The bicycle frame is connected to a wire that gives it the opposite charge (-ve)

They’ll be attracted to the bicycle frame’s surface

33
Q

How do inkjet printers work?

A

Each drop of ink is given a charge so that as it falls between a pair of deflecting plates, electrostatic forces direct it to the correct position on the paper.

The charges on these plates change 100s of times per second to direct each drop of ink to its specific position, forming pics and texts.

34
Q

How do photocopiers work?

A

+ve charge is sprayed onto a turning drum covered in selenium. A bright light is shone on the paper to be copied. The white parts of the paper reflect light onto the drum, the selenium loses charges in places where light is reflected.

A -vely charged toner is blown across the drum and attaches to the +vely charged parts of the drum.

The paper is pressed against the drum and picks up the pattern of the toner. The toner is permanently fixed in place by heating the paper

35
Q

How do electrostatic precipitators work?

A

As the smoke rises up the chimney, it passes through a mesh of highly charged wires.

A -ve charge is induced on the dust and ash particles, as these particles rise they are attracted to large metal earthed plates

36
Q

Problems with static electricity:

A
  • The risk of electrocution (from lightning)

- The risk of a fire or explosion (due to a spark close to flammable gas or liquid).

Physics (8 decks)

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