Electricity

Question 1

what is current measuresd in?

Answer 1

amperes

Question 2

what is electric current defined as?

Answer 2

the reate of flow of charge

Question 3

what does ‘Q’ stand for in I = Q/t

Answer 3

the charge transferrred in coulumbs

Question 4

what is 1A equal to in words

Answer 4

the amount of charfe passing a given point in a circuit per unit of time

Question 5

A charge of 0.26 MC passes through a heater in 6.0 hours. Calculate the average current in the heater in that time, giving your answer to an appropriate number of significant figures.

Answer 5

I = (0.26x10^6)/(6.0x3600)
I = 12A (2sf)

Question 6

what is electrical charge measured in?

Answer 6

coulumbs

Question 7

what is electrical charge / define coulumb

Answer 7

charge flowing past a point in one second when there is an electrical current of 1A

Question 8

what is a particle with electrical charge called

Answer 8

a charge carrier

Question 9

what is ‘e’ and what does it stand for

Answer 9

1.60x10^-19, elementary charge

Question 10

what ‘e’ does a proton have

Answer 10

+1e

Question 11

what ‘e’ does an electron have

Answer 11

-1e

Question 12

what can the size of the charge on an object be expressed as?

Answer 12

a multiple of ‘e’

Question 13

what is the net charge given by and what does each variable stand for?

Answer 13

Q = ±ne,
Q –> net charge in C,
n –> number of electrons
e –> elementary charge

Question 14

what do we describe charge on the object as being? and why?

Answer 14

‘quantised’,
charge can only be multiples of ‘e’,
for example:
1.92 x10^-18C –> +12e

Question 15

calculate the charge in coulumbs for these charges:
+2.0e
-12e

Answer 15

3.2 x 10^-19C
-1.9 x 10^-18C

Question 16

A rechargeable battery pack is labelled 5000 mA h. Calculate how much charge the pack can deliver when fully charged

Answer 16

1 As is equivalent to 1 C

1.0 mAh = 1.0 x 10^-3 Ah = 60 x 10^-3 A min = 3.6 As; therefore, 1.0 mAh = 3.6 C

5000 mAh = 5000 x 3.6 = 18000 C

Question 17

What do charge carriers tend to be in liquids?

Answer 17

ions

Question 18

what is the structure of a metal?

Answer 18

a lattice of positive ions ssurrounded by a number of free electrons (delocalised electrons) which vibrate more vigourously as the temperature of a metal increases

Question 19

what may a larger current be due to?

Answer 19

• a greater number of electrons
  passing a given point in a second
• the same number of electrons moving faster through the metal

Question 20

what direction is conventional current in?

Answer 20

positive terminal –> negative terminal

Question 21

wwhat are liquids that can carry current called? and what is current in this case known as?

Answer 21

electrolytes
the flow of ions

Question 22

how do we measure current

Answer 22

using an ammeter

Question 23

why should ammeters have the lowest resistance possible?

Answer 23

to reduce the effect on the current

Question 24

outline the difference between conventional current and electron floww in a wire

Answer 24

Conventional current is from the positive terminal to the negative terminal.
Electrons flow from the negative terminal to the positive terminal.

Question 25

Describe the similarities and differences between electric current in a metal wire and in an ionic solution.

Answer 25

Similarities: Both are examples of flows of charge. Differences: In metals the charge carriers are electrons. In ionic solutions the charge carriers are ions. In metals the charge carriers are negative. In ionic solutions the charge carriers can be positive or negative.

Question 26

A solution of magnesium chloride contains Mg2+ and Cl- ions. Calculate the current in the cathode in µA when 6.0 x 10^14 cations come into contact with the cathode in 3.0 minutes.

Answer 26

- I = Q/t and Δt = 3.0 minutes = 180 s [1] - Each cation has a relative charge of +2e. ΔQ = 2 x 1.60 x 10^-19 x 6.0 x 10^14 = 1.9 x 10^-4 C [1] I = 1.9 x 10^-4 / 180 = 1.1 x 10^-6 A = 1.1 μA (2 s.f.) [1]

Question 27

wwhat is the conservation of charge?

Answer 27

electrical charge cant be created or destroyed

Question 28

what is kirchoffs 1st law?

Answer 28

the sum of currnets into that point is equal to the sum of currents out of that point

Question 29

waht is the number density

Answer 29

the number of free electrons per cubic metre of material

Question 30

what does it mean if the number density is higher

Answer 30

the greater number of electrons leads to better electrical conduction

Question 31

do conductors have hign number of number density?

Answer 31

yes

Question 32

do insulators hace a high value of number density?

Answer 32

no

Question 33

how can the number density of semiconductor be described as?

Answer 33

between the densities of conductors and insulators

Question 34

what do the electrons in semiconductors need to do to carry the same current as metals + what does this lead to?

Answer 34

the need to move faster, leads to and increase in temperature

Question 35

what do most charge carriers do to conduct electricity

Answer 35

they moce slowly colliding with the +ve metal ions whilst drifting towards the +ve terminal all at once

Question 36

wht is the equation that links I , A, n, e v?

Answer 36

I = Anev I --> current (amperes) A --> cross sectional area of conductor n --> number density e --> 1.60 x 10^-19 C v --> mean drift velocity of charge carriers (ms^-1)

Question 37

how can we get a graeter drift velocity

Answer 37

reducring the cross sectional area

Question 38

define battery

Answer 38

two or more cells connected in series

Question 39

what is potential difference

Answer 39

measure of the transfer of energy by charge carriers

Question 40

what is 1 volt

Answer 40

when 1J of energy is tranferred per unit charge passing through the component - 1000V = 1000J transferrend per C of charge

Question 41

what is emf

Answer 41

used to describe when work is doen on the charge carriers

Question 42

what iss resistance

Answer 42

resisting the flow of charge carriers

Question 43

define ohm

Answer 43

resistance of a componenet when a pd of IV is produced per ampere of current

Question 44

define resistivity

Answer 44

describes the elecctrival property of a maaterial

Question 45

how to calculate resistance from resistivity

Answer 45

R = ρL / A where: R is the resistance of the material (in ohms, Ω) ρ is the resistivity of the material (in ohm-meters, Ωm) L is the length of the material (in meters, m) A is the cross-sectional area of the material (in square meters, m²)

Question 46

what is kirchoff second law

Answer 46

sum of emf = sum of pdss around a closed loop