Current and Charge

Question 1

What must there be for electrical current to flow?

Answer 1

a complete circuit and potential difference

Question 2

What did physicists discover about conventional current?

Answer 2

it flows negative to positive

Question 3

What is two quantities are the same in terms of electrons per second?

Answer 3

current and charge

Question 4

What is the charge of an electron?

Answer 4

1.6 x 10^-19

Question 5

What is charge in terms of electrons?

Answer 5

number of electrons x charge of one electron

Question 6

In which particles is charge the fundamental property?

Answer 6

protons and electrons

Question 7

Define charge carriers:

Answer 7

any charged particle that can move

Question 8

What happens when charge carriers move?

Answer 8

transfer energy from the source to the component

Question 9

Define current:

Answer 9

rate of flow of charge

Question 10

What analogy is used for ‘electrons flowing in a circuit’?

Answer 10

balls flowing through a hollow pipe

Question 11

What analogy is used for ‘the cell pushes electrons in the wire’?

Answer 11

an engine pushes balls in the pipe

Question 12

What analogy is used for ‘when electrons go through the bulb or a resistor, they cause the wire to heat up’?

Answer 12

when the balls have to be squeezed through a thin section of the pipe they make the pipe hot

Question 13

What analogy is used for ‘when the cell runs out the current stops flowing’?

Answer 13

when the engine runs out of fuel it will stop pushing the balls

Question 14

What analogy is used for ‘measuring the current is counting the number of coulombs passing a certain point in the circuit each second’?

Answer 14

watching the number of balls passing a certain point of the pipe each second

Question 15

What analogy is used for ‘the current is the same everywhere in the circuit’?

Answer 15

number of balls entering narrow strip= number of balls exiting narrow strip, speed of balls is constant

Question 16

What analogy is used for ‘adding another cell will increase current’?

Answer 16

adding another motor will speed up the balls in the pipe

Question 17

What analogy is used for ‘adding another resistor reduces current but it still remains the same across the circuit’?

Answer 17

adding an obstruction in the pipe will make the balls go slower

Question 18

What analogy is used for ‘sum of current entering a point=sum of current leaving a point’?

Answer 18

number of balls entering a junction = number of balls leaving a junction

Question 19

What did Milikan’s Oil Drop Experiment find?

Answer 19

calculated that the charge of an electron was about 1 x 10^-19 coulombs

Question 20

What is the method of Milikan’s Oil Drop Experiment?

Answer 20

• oil mist produced by atomiser is sent through a plate of electrical condensor
• rate of fall measured through micrometer and can be controlled by the plate’s voltage
• X-Rays passed through the chamber ionise the air inside where the droplets acquire charge

Question 21

What forces act on the oil drip in Milikan’s Oil Drop Experiment?

Answer 21

gravitational, electrostatic, viscous drag

Question 22

What observations came from Milikan’s Oil Drop Experiment?

Answer 22

• charge on droplets is always a multiple of electron charge
• Q=ne
• charge of electron = 1.6 x 10^-19
• mass of electron is combination of Thompson and Milikan

Question 23

Define potential difference:

Answer 23

energy supplied by the cell

Question 24

1 Volt is…

Answer 24

when 1C of charge transfers 1J of energy potential difference is 1V

Question 25

What is Kirchoff’s first law?

Answer 25

total current flowing into a point = total current flowing out a point

Question 26

What is Kirchoff’s second law?

Answer 26

in a closed loop circuit potential difference across all components = 0

Question 27

How are Kirchoff’s laws verified?

Answer 27

• in a series circuit more components = decreased potential difference because resistance increases
• resistance increases as current decreases as current remains the same across the circuit

Question 28

Define number density:

Answer 28

number of free charge carriers per unit volume

Question 29

Which materials have the highest number density?

Answer 29

conductors

Question 30

Which materials have the lowest number density?

Answer 30

insulators

Question 31

How does the cross sectional area impact mean drift velocity?

Answer 31

narrower wire gives greater drift velocity in order for current to remain the same

Question 32

What is the relationship between mean drift velocity and cross sectional area?

Answer 32

inversely proportional