Electric Charge, Current and Voltage

Question 1

What is an electrical conductor?

Answer 1

A material in which current flows through easily.

Question 2

Name some good conductors.

Answer 2

Metals, graphite, salt solutions or molten salts.

Question 3

What is an electrical insulator?

Answer 3

Electrical insulators have a high resistance to the flow of electric current.

Question 4

Give some examples of insulators.

Answer 4

Plastic, dry wood, glass and rubber.

Question 5

Gold and silver are better conductors than copper, so why is copper used in wires?

Answer 5

Copper is used in pipes because it is a very good conductor of electricity and fairly inexpensive in comparison to silver and gold.

Question 6

What is a series circuit?

Answer 6

One in which all the components are connects end to end.

Question 7

How do you calculate current in a series circuit?

Answer 7

It is the same everywhere so place an ammeter anywhere.

Question 8

How is the voltage dispersed across a series circuit?

Answer 8

The voltage splits up so that the sum of the voltage across the individual components is equal to the voltage of the power supply or battery.

Question 9

What is a parallel circuit?

Answer 9

A circuit in which all the components are connected side by side.

Question 10

How is the voltage dispersed across a parallel circuit?

Answer 10

The voltage is the same across each branch.

Question 11

How is the current dispersed across a parallel circuit?

Answer 11

The current splits up so that the sum of the currents in each branch will add up to the current supplied by the battery or power supply.

Question 12

Which circuits are Christmas tree lights connected in? Why?

Answer 12

Series so that small, low voltage bulbs can be used. However this means that if one bulb breaks the whole thing stops working.

Question 13

Which circuits are the lights in your home? Why?

Answer 13

Parallel so each bulb can be switched on and off separately and the brightness of one bulb does not change whether some bulbs are on or off. Also if one bulb breaks or is removed you can still use the other ones.

Question 14

What is current?

Answer 14

The rate of a flow of charge.

Question 15

What is the relationship between charge, current and time?

Answer 15

Charge = current*time Q = I*t

Question 16

What is charge measured in?

Answer 16

Coulombs (C)

Question 17

What is current measured in?

Answer 17

Amps (A)

Question 18

What causes current In a metal wire?

Answer 18

The flow of electrons from the negative terminal of the battery/power supply from which they are repelled to the positive terminal from which they are attracted.

Question 19

What are the two types of charges and what is the rule between them?

Answer 19

Positive and negative and the rule is:

Unlike charges attract (i.e. positive and negative)

Like charges repel (i.e. positive and positive)

Question 20

Uses of static electricity:

Answer 20

Inkjet printers: charging ink droplets in inkjet printers allows the droplets to be directed to particular places on the paper by deflecting them between charged plates.

Photocopiers: A statically charged drum is exposed to light, reflected from the document to be copied, which discharges the drum everywhere except where the dark print does not reflect light. The charged parts of the drum attract the toner which is the transferred to the printing paper. Heat then bonds to the printing paper.

Paint Spraying: The tiny droplets of pait are given a static charge and the onject to be painted is connected to a supply of opposite charge. This causes the paint droplets to be attracted to the object being painted and the amount of paint wasted is drastically reduced and a more even finished product.

Question 21

Problems with static electricity:

Answer 21

Electric shocks

Fuelling tankers and aircraft

Handling microprocessors and computer ‘chips’

Question 22

How are electric shocks a problem with static electricity?

Answer 22

Cars become charged with static electricity, particularly on dry days, and can give an unpleasant shock when someone touches the car. This also happens while walking on acrylic carpets.

Question 23

How can fuelling tankers and aircraft be effected by static electricity in a negative way?

Answer 23

When fuelling it is possible for static charge to build up on planes or taners and, should a spark occur, a fire or explosion could result. This is prevented by ensuring a plane or tanker is electrically earthed to discharge them.

Question 24

How is handling microprocessors and computer ‘chips’ problematic when it comes to static electricity?

Answer 24

Workers handling electronic components must take care not to become charged by static as this can easily destroy expensive components. They wear earthing straps and work on earthed metal benches to prevent this.

Question 25

What is voltage? What is it measured in?

Answer 25

The ‘strength’ of energy sources, measured in volts.

1 volt means 1 joule per coulomb

This means a 12V car battery supplied 12J of energy to each coulomb of charge that circulates.

Question 26

How do you measure current in a circuit? What does it tell you?

Answer 26

Current is the same throughout a circuit so an ammeter can be placed anywhere. This means it is part of the circuit and so it should have a very low resistance otherwise it will make the current in the circuit smaller.

It tells you how many coulombs of charge are passing through the circuit each second.

Question 27

How do you measure voltage in a circuit?

What does this tell you?

Answer 27

The voltagae is measured using a voltmeter places in parallel with the component through which the curent is flowing. This tells you how many joules of energy are being converted (when it is across a lamp) into heat and light per coulomb of charge passing through that lamp. Voltmeters have a very large resistance

Question 28

Descibe the electrical circuit symbol of a switch:

Answer 28

line, blank circle, the continued line then blank circle, the continued line (for closed)

Line opened when opened

Question 29

Descibe the electrical circuit symbol of a fuse:

Answer 29

empty square with line through it

Question 30

Descibe the electrical circuit symbol of an LED:

Answer 30

empty triangle on a line with tip facing the right, touching a vertical line, arrows pointing north east on top.

Question 31

Descibe the electrical circuit symbol of a variable resistor:

Answer 31

empty rectangle on a line with a single arrow going through it with the tip facing north east

Question 32

Descibe the electrical circuit symbol of an indicator lamp

Answer 32

circle with a cross on a line

Question 33

Descibe the electrical circuit symbol of a diode

Answer 33

triangle facing south on a line, touching a verticle line

Question 34

Descibe the electrical circuit symbol of a thermistor

Answer 34

rectangle on a line with a line going through it north east but on the bottom line of the rectangle the line is parallel (hard to explain, look it up).

Question 35

Descibe the electrical circuit symbol of a light dependent resistor (LDR)

Answer 35

rectangle when with arrows on top pointing south east