Chapter 8 Charge and Current

Question 1

What is electric current?

Answer 1

rate of flow of charge, measured in Amperes

Question 2

How is current measured in a circuit?

Answer 2

Ammeters in series

Question 3

What is charge?

Answer 3

a physical characteristic

Question 4

What is conventional current?

Answer 4

the flow from positive to negative, direction of current in a circuit

Question 5

What is a conductor?

Answer 5

a material that allows the flow of electrical charge. Good conductors have a large amount of free charge carriers to carry a current

Question 6

What are electrolytes?

Answer 6

Substances that contain ions that when dissolved in a solution, act as charge carriers and allow current to flow.

Question 7

What is electron flow?

Answer 7

The opposite direction to conventional current flow. Electrons flow from negative to positive

Question 8

What is elementary charge?

Answer 8

The smallest possible charge, equal to the charge of a proton.

Question 9

What is the value of elementary charge?

Answer 9

1.60 x10^-19C

Question 10

What are insulators?

Answer 10

A material that has no free charge carriers and so doesn’t allow the flow of electrical charge.

Question 11

What is Kirchhoff’s First Law?

Answer 11

A consequence of the conservation of charge. The total current entering a junction must equal the total current leaving it.

Question 12

What is mean drift velocity?

Answer 12

The average velocity of an electron passing through an object. It is proportional to the current, and inversely proportional to the number of charge carriers and the cross-sectional area of the object.

Question 13

What is the quantisation of charge?

Answer 13

The idea that charge can only exist in discrete packets
of multiples of the elementary charge.

Question 14

What are semiconductors?

Answer 14

A material that has the ability to change its number of charge carriers, and so its ability to conduct electricity. Light dependent resistors and thermistors are both examples.

Question 15

What is the equation for current, charge and time?

Answer 15

I = Q/t

Question 16

How do you calculate the net charge on an object?

Answer 16

Q = +/- ne

Question 17

What is millikan’s experiment?

Answer 17

Motion of an electrically charged oil droplet between two oppositely charged parallel plates. Oil droplets falling through the air experienced gravitational force, air resistance and upthrust.

Question 18

What is the structure of a metal?

Answer 18

regular crystal structure OR lattice of positive ions, surrounded by delocalised electrons

Question 19

What produces a larger current?

Answer 19

• greater number of electrons moving past a given point each second
• same number of electrons moving faster through a metal

Question 20

What is a positive electrode called?

Answer 20

anode

Question 21

What is a negative electrode called?

Answer 21

cathode

Question 22

Why are ammeters placed in series?

Answer 22

so they have the lowest possible resistance, reduce effect of current.

Question 23

What would happen with an ammeter with high resistance?

Answer 23

decrease the current its measuring

Question 24

What is an ideal ammeter?

Answer 24

has zero resistance, no effect on the current it measures

Question 25

What is the conservation of charge?

Answer 25

electrical charge can neither be created nor destroyed, constant in the universe

Question 26

What is the equation for Kirchhoff’s first law?

Answer 26

sum of current in = sum of current out

Question 27

What is number density?

Answer 27

number of free electrons per cubic meter of material, higher means better electrical conductor

Question 28

What are charge carriers?

Answer 28

electrically charged particles, free to move in an object

Question 29

How fast do charge carriers move?

Answer 29

slowly. free electrons repeatedly collide with metal ions as they drift, when switch on, they start moving all at once

Question 30

What is another equation from current?

Answer 30

I = A n e V
(area x number density x elementary charge x mean drift velocity)

Question 31

How are current and wire cross section linked?

Answer 31

current is directly proportional to the cross sectional area of a wire

Question 32

What happens if you half the radius of a wire?

Answer 32

the velocity of the electrons quadruple

Question 33

What concepts does Kirchhoff’s first law deal with?

Answer 33

electrical current: any point in an electrical circuit, the sum of the currents into that point = sum of currents out of that point

Question 34

What does Kirchhoff’s law conserve?

Answer 34

charge

Question 35

Do semiconductors or metals have a higher number density?

Answer 35

metals

Question 36

How do make semiconductors carry the same current as metals?

Answer 36

make the electrons move faster

Question 37

What happens when you switch on a lamp?

Answer 37

charge carriers, like electrons move SLOWLY and free electrons constantly collide with the metal ions and drift to the positive terminal. They start moving at once, so quick light on

Question 38

What is the other equation for electric current?

Answer 38

I = A n e v
(cross-sectional area x number density x elementary charge x mean drift velocity)