Current of Electricity (16)

Question 1

How can an electric current flow through a conductor

Answer 1

An electric current can flow through a conductor as it consists of free-moving electrons.

Question 2

How can energy from the voltage source be transferred

Answer 2

Energy from the voltage source can be transferred by the flow of charges through a closed circuit but not an open circuit.

Question 3

Define current

Answer 3

Rate of flow of electric charge

Question 4

SI unit of electric charge

Answer 4

Coulomb (C)

Question 5

SI unit of current

Answer 5

Ampere (A)

Question 6

Relationship between Charge and protons/neutrons

Answer 6

Each electron/proton has the same amount of charge of 1.6 x 10 ^-19C. Thus 1 C of charge is approximately equal to 6.25 x 10 ^18 electrons/protons.

Question 7

Formula for Current

Answer 7

I = Q/t

Question 8

What is a conventional current

Answer 8

Conventional current is the flow of charges from the positive terminal of the battery to the negative terminal of the battery

Question 9

What is an electron flow

Answer 9

Electron flow is the flow of electrons from the negative terminal of the battery to the positive terminal

Question 10

Define Electromotive Force (e.m.f)

Answer 10

Electromotive force (e.m.f., ɛ or E) of an electrical source is the work done by the source in driving a unit charge around a complete circuit.

Question 11

Define Potential difference (p.d.)

Answer 11

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

Question 12

Formula of Work done/ W(joules), using V

Answer 12

V = work done/ Q

Question 13

What is the relationship of V

Answer 13

The SI unit of e.m.f. and potential difference (p.d.) are measured in volt (V).
1 V is equivalent to 1 J/C.

Question 14

Difference between emf and pd 1

Answer 14

e.m.f is the work done to move each unit charge through the circuits

P.d is the work done by each unit charge passing through the components

Question 15

Difference between e.m.f and p.d 2

Answer 15

E.m.f is present even when no current is drawn through the source

P.d across any electrical component is 0 in the absence of current

Question 16

What is used to measure e.m.f and p.d

Answer 16

E.m.f. and p.d. are measured by a Voltmeter connected in parallel across the two points to be measured.

Question 17

Why does the electrical resistance of metals increase with temperature?

Answer 17

When electrons flow through a component, they collide with the ions of the components and with other electrons. These collisions resist the flow of the electrons.

Question 18

Formula for resistance

Answer 18

R = V/I

Question 19

SI unit for resistance

Answer 19

Ohm (Ω)

Question 20

What are the factors affecting resistance of a conductor

Answer 20

o ρ - resistivity (Ωm) – depends on the material

o l - length (m)

o A - cross-sectional area (m 2 ) – depends on the thickness of the wire

Question 21

Why does the resistance increase when the length of the wire is longer

Answer 21

The longer the cylinder, the more collisions the electrons will make with its atoms.
Hence, the resistance of the wire is directly proportional to the length

Question 22

Why does the resistance increase when the cross-sectional area of the wire is larger

Answer 22

The larger the cross-sectional area of the cylinder, the greater the number of electrons that can flow through it.
Therefore, The resistance is inversely proportional to the area of the cylinder

Question 23

Formula for R, using csa

Answer 23

Resistance = (Resistivity, p x length l ) / Cross-sectional area (A)

Question 24

Define ohms law

Answer 24

Ohm’s Law states that: The current passing through a metallic conductor is directly proportional to the potential difference across its ends, provided the physical conditions (such as temperature) are constant. (I  V)

Question 25

What are ohmic conductors

Answer 25

Ohmic conductors are conductors that obey Ohm’s Law. This means that the resistance of an ohmic conductor is constant. Many metals and resistors are ohmic conductors when temperature is constant.

Question 26

What are Non-ohmic conductors

Answer 26

Non-ohmic conductors – do not obey Ohm’s law. I and V are not proportional.

Question 27

describe the graph for filament lamp and thermistors (same graphs)

Answer 27

V-I graph : curved, accelerating graph (look like n, top left of O

I-V graph : curved go up, decelerating graph (look like bottom right of O)

Question 28

Describe the graph of a Semiconductor diode

Answer 28

unique one where it starts below the line then goes up