12.1 Electric current

Question 1

What must there be to make an electrical current pass round a circuit

Answer 1

must be a complete circuit

must be a source of potential difference in the circuit e.g battery

Question 2

what is the electric current

Answer 2

the rate of flow of charge in the wire or component

Question 3

the current is due to the passage of what

Answer 3

charged particles known as charge carriers

Question 4

what are the charge carriers in metals

Answer 4

conduction electrons

they move around inside the metal repeatedly colliding with eachother and the fixed positive ions in the metal

Question 5

what are the charge carriers in a salt solution

Answer 5

charge is carried by ions which are charged atoms or molecules

Question 6

what happens if the test material is a metal

Answer 6

the charge carrier in all part of the circuit are electrons

Question 7

what way round do the electrons go around a circuit

Answer 7

the electrons enter the battery through the battery at its positive terminal after passing through eh metal and the ammeter and leave at the negative terminal to continue the cycle again

Question 8

where is the convention for the direction of current in a circuit

Answer 8

from positive to negative terminal

Question 9

when was the convention agreed

Answer 9

long before the discovery of electrons

when it was set up it was known that an electric current id a flow of charge one way around a circuit.

however they didnt know wether the current was due to a positive or negative charge flowing around the circuit

Question 10

what is the unit of current

Answer 10

Ampere (Amps) A

which is defined in terms of magnetic force between to parallel wires when the carry the same current

Question 11

what is the symbol for current

Answer 11

I

Question 12

what is the unit of charge

Answer 12

Coulomb (C)
equal to the flow of charge in one second when the current is one Amp

Question 13

what is the symbol for charge

Answer 13

Q

Question 14

what does delta charge equal

Answer 14

deltaQ = I Delta t

Question 15

what does the equation I = deltaQ/Delta t show

Answer 15

the current of 1 Amp is due to the flow of charge of 1 coulomb per second

as magnitude of the charge of electrons is 1.6 x 10^-19 C

a current of 1 A along the wire must be due to 6.25x10^18electrons passing a long the wire each second

1/1.6x10^-19

Question 16

what happens within an insulator

Answer 16

each electron is attached to an atom and cannot move away from it

when voltage is applied across an insulator no current pass through it because no electrons can move through the insulator

Question 17

what happens within a metallic conductor

Answer 17

most electrons are attached to atoms however some are delocalised

the delocalised electrons are the charge carriers

when a voltage is applied across the metal the conduction electrons are attracted toward the positive terminal of then metal

Question 18

what happens within a semi conductor

Answer 18

number of charge carries increases with an increase in temperature

the resistance of the semiconductor therefore decreases as the temperature is raised

a pure semi conductor material is referred to as an intrinsic semiconductor because conduction is due to electrons that break free from atoms of the semiconductor