Charge + Current

Question 1

current

Answer 1

rate of flow of charge

Question 2

elementary charge

Answer 2

the charge on 1 proton (1.6 * 10^-19)

Question 3

electric current in a wire

Answer 3

lattice of positive ions with free electrons.

Question 4

reasons for a larger current

Answer 4

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

Question 5

conventional current

Answer 5

positive to negative

Question 6

what are electrolytes

Answer 6

liquids that carry an electric current with anode (positive electrode) and cathode (negative electrode). the movement of the ions to the electrodes is a flow of charge so there’s an electric current.

Question 7

kirchoffs 1 law

Answer 7

for any point in an electric circuit. sum of currents into that point is equal to the sum of currents out of that point/

Question 8

number density in conductors

Answer 8

higher the no. densoty the greater the number of free electrons so the better the electrical conductor.

Question 9

definition for a volt

Answer 9

the pd across a component when 1j of energy is transferred per unit charge passing through the component.

Question 10

emf

Answer 10

the energy transferred from chemical energy to electrical energy per unit charge.

when work is done ON the charge carriers. charges gain energy as they pass through a cell.

Question 11

emf equation

Answer 11

e = w/q

Question 12

how do electron guns work

Answer 12

small metal filament heated, electrons gain enough kinetic energy to escape from the surface of the metal which is thermionic emission. when filament placed in vacuum and high pd applied between it and an anode, filament becomes a cathode. electrons accelerate towards anode and become a beam. zapppp.

Question 13

electron gun equation

Answer 13

wd on electron = gain in KE
eV = 1/2mv^2

Question 14

ohm definition

Answer 14

the resistance of a component when a pd of 1v is produced per ampere of current.

Question 15

ohms law

Answer 15

for a metallic conductor kept at a constant temperature the current in the wire is directly proportional to the pd.

Question 16

tempereature and resistance

Answer 16

as temp increases the positive ions inside the wire have more internal energy, they vibrate more, have more collisions, and the charge carriers do more work so resistance increases.

Question 17

diodes and ohms law

Answer 17

diodes are non-ohmic + resistance of a diode is not constant

Question 18

what affects resistance in a wire

Answer 18

• material of the wire
• length of the wire
• cross-sectional area of the wire

Question 19

unit for resistivity

Answer 19

ohm metre

Question 20

define resistivity

Answer 20

resisitivity of a material at a given temperature is the product of the resistance of a component made of the material and cross sectional area divided by length.

Question 21

resistivity and temperature

Answer 21

as temperature increases resistivity increases

Question 22

how to calculate resistivity from graph

Answer 22

is graph is R against L then gradient is p/A and times with cross-sectional area of wire

Question 23

what is a negative temperature coefficient

Answer 23

the resistance drops as the temperature increases e.g. thermistor

Question 24

filament lamp resistance

Answer 24

as current increases, electrons transfer energy to the positive ions which raises the temperature causing an increase in resistance

Question 25

thermistor resistance

Answer 25

increase in temperature leads to increase in number density of the free electrons so resistance decreases.

Question 26

LDR resistance

Answer 26

made from a semiconductor in which the number density of charge carriers depends on the intensity of the incident light. dark conditions - high resistance. light - no. density increases so resistance decreases.

Question 27

define power

Answer 27

the rate of the energy tansferred

Question 28

power equations

Answer 28

P = VI
P= I^2 R
P = V^2/R

Question 29

costs depends on

Answer 29

• power of the device + how long it’s used for