current electricity & DC circuits (I)

Question 1

what does 1A mean

Answer 1

1A = 1Cs^-1

charge of 1C flowing in the circuit in 1s

Question 2

one coulomb

Answer 2

quantity of electric charge that flows past a given point in a circuit when a steady current of 1 ampere flows for one second

Question 3

how many electrons in 1C

Answer 3

6.25x10^18

Question 4

charge on one electron

Answer 4

1.60x10^-19 C

Question 5

1 milliamperes (mA)

Answer 5

1x10^-3 A

Question 6

1 microampere

Answer 6

1x10^-6 A

Question 7

what is the cause and effect in a circuit

Answer 7

cause: voltage
effect: current

Question 8

role of battery in the circuit

Answer 8

• give energy to the electrons so that they can flow and be a current
• provides a potential diff

Question 9

electromotive force (e.m.f)

Answer 9

defined as the energy converted from non-electrical forms to electrical forms when one coulomb of charge passes through the cell

Question 10

what does 1V mean

Answer 10

e.m.f. of 1V means that it takes 1J of work to bring 1C of charge from the positive end to negative end of a circuit

Question 11

potential difference (p.d.)

Answer 11

defined as the energy converted from electrical forms to other forms of energy when one coulomb of charge passes from one point to another point

Question 12

difference between potential, voltage and e.m.f., p.d.

Answer 12

potential & voltage w reference to 1 pt

e.m.f. & p.d. w reference to 2 pts

Question 13

resistance

Answer 13

ratio of the potential difference V across the conductor to the current I flowing through it

(in terms of motion of electrons)

resistance in the resistor is caused by the collision of free electrons with the vibrating atoms/ions in their path (under an applied potential difference)

Question 14

state ohm’s law

Answer 14

ohm’s law states that the current flowing in a metallic conductor is directly proportional to the potential difference across its ends, provided the physical conditions are constant

(eg. temperature)

Question 15

ohmic conductor

Answer 15

obeys ohm’s law

• relation between I and V is linear
• graph is a straight line passing through origin

Question 16

non-ohmic conductor

Answer 16

does not obey ohm’s law

• relation between I and V is not linear
• graph is not a straight line passing through the origin

Question 17

thinner wire vs thicker wires (resistance)

Answer 17

thinner wire -> higher resistance than thicker

Question 18

longer wire vs shorter wire (resistance)

Answer 18

longer wire -> higher resistance than shorter wire

Question 19

what is meant by a “current of 0.70A”

Answer 19

means that a total charge of 0.70C is flowing through every point in the circuit in 1s

Question 20

is the bulb an ohmic conductor (no)

Answer 20

no
for ohmic conductor, the current I is proportional to the voltage V. from the graph, the graph gradient is not constant, hence I is not proportional to V, hence the conductor is not ohmic

Question 21

state one possible source of error in this experiment and explain how its effect can be minimised

• is an ohmic conductor but results show otherwise
• ohm’s law: temp must b constant

Answer 21

the temp of the bulb/wire may change as the reading is being taken

this will result in a variation of the bulb’s resistance

the switch should only be closed when readings are taken

Question 22

when switch S is open, ammeter reading is 0

e.m.f. 16v

state the value of the potential diff across switch s when it is open/closed

Answer 22

closed: 0V
open: 16V

Question 23

explain what the value of potential difference across the switch means (0V and 16V when closed and open)

Answer 23

1. 0V of electrical energy required to drive 1C of positive charge across the switch since the switch has negligible resistance when the switch is closed
2. when the switch is open, 16V is actually measuring the p.d. across the cell

Question 24

electric current

Answer 24

measure of the rate of flow of electric charge through a given cross-section of a conductor