Ch 13 Electric Charge and Current of Electricity#

Question 1

What types of charges are there in static electricity?

Answer 1

positive and negative charges.

Question 2

What is the SI unit for charges?

Answer 2

coulomb (C)

Question 3

What is the difference between a neutral object and a negatively charged object?

Think in terms of no. of protons and electrons.

Answer 3

A neutral object contains equal number of protons and electrons.
A negatively charged object contains more electrons than protons.

The same can be compared for a positively charged object.

Question 4

Define the law of electrostatic.

Answer 4

Like charges repel.
Unlike charges attract.

Question 5

What is an electric field?

Answer 5

A region where an electric charge experience an electric force.

Question 6

Define current.

Answer 6

Current is the rate of flow of electric charge.

Question 7

What is the SI unit of current?

Answer 7

Ampere (A)

Question 8

What is the instrument used to measure current in a circuit?

Answer 8

Ammeter / digital multi-meter

Question 9

How should the ammeter be connected in a circuit?

Answer 9

connected in series

Question 10

What is the name given to this type of current flow?

Answer 10

Elecron flow

Take note of how the current’s direction with respect to the termials of the battery.

Question 11

What is the name given to this type of current flow?

Answer 11

Conventional current

Take note of how the current’s direction with respect to the termials of the battery.

Question 12

What is the relationship between I, Q and t?
(in other words the formula)
[Please recall what I, Q and t represents]

Answer 12

Q = It

Question 13

Define electromotive force (e.m.f.).

Answer 13

Electromotive force (e.m.f.) is the amount of work done by a source (e.g. battery, cell) in driving a unit charge around a complete circuit.

Question 14

Define potential difference (p.d).

Answer 14

Potential difference (p.d.) across a component in a circuit is the work done to drive a unit of charge through the component.

Question 15

What is the SI unit of electromotive force (e.m.f.)?

Answer 15

Volt (V)

Question 16

What is the SI unit of potential difference (p.d)?

Answer 16

Volt (V)

Question 17

What is the instrument used to measure voltage across a component in a circuit?

Answer 17

voltmeter / digital multi-meter

Question 18

How should the voltmeter be connected in a circuit?

Answer 18

connected in parallel to the component

Question 19

What is the relationship between V, W and Q?
(in other words the formula)
[Please recall what V, W and Q represents]

Answer 19

W = VQ

Question 20

Define resistance.

Answer 20

Resistance of a component is the ratio of voltage to current in a component.

Question 21

What is the relationship between R, V and I?
(in other words the formula)
[Please recall what R, V and I represents]

Answer 21

R = V / I

Question 22

What is the SI unit of resistance?

Answer 22

ohm (Ω)

Question 23

What are the factors that affect the resistance of a wire?

[There are 4 factors.]

Answer 23

1) length of wire (l)
2) cross-sectional area of wire (A)
3) resistivity of the material (ρ)
4) temperature of wire

Question 24

State how the length of wire affects the resistance.

Answer 24

The longer the wire, the larger the resistance.

Question 25

State how the thickness of wire affects the resistance. | thickness also means cross-sectional area of wire

Answer 25

The thicker the wire, the lower the resistance. | The thinner the wire, the higher the resistance.

Question 26

State how temperature of a wire affects its resistance.

Answer 26

The higher the temperature, the larger the resistance.

Question 27

Define Ohm's Law.

Answer 27

Ohm's law states that the current through a metallic conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and other physical conditions remains constant.

Question 28

Explain why the filament lamp does not obey Ohm's law.

Answer 28

As current flows through the filament lamp, it heats up and increases the resistance of the filament lamp.

Question 29

What are the 2 factors on a VI graph that shows an electrical component obeys Ohm's law? (i.e. what are the 2 things to look out for in a VI graph?

Answer 29

1) The graph must be a straight line. 2) The line must pass through the origin.