Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

physics module 4 - electrons, waves and photons > Energy, power and resistance > Flashcards

Energy, power and resistance Flashcards

1
Q

what is a battery

A

two or more cells connected end to end or in series

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are the circuit symbols need to know

A

switch open
switch closed
cell
bettery
diode
resistor
variable resistor
lamp
fuse
voltmeter
ammeter
thermistor
LDR
LED
capacitor
single cell
two cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is potential difference

A

measure of the transfer of energy by charge carriers
the energy transferred from electrical energy to other forms per unit charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is potential difference measure in

A

volts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is a volt

A

the pd across a component when 1J of energy is transferred per unit chare
1V=1JC^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is the equation for potential difference

A

V=W/Q

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is used to measure pd

A

voltmeter
connected in parallel across a particular component

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what properties should a voltmeter have

A

infinite resistance so when connected no current passes through the voltmeter itself

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is electromotive force

A

the enrgy transferred from chemical energy to electrical energy per unit charge
describe when work done on the charge carriers
charges are gaining energy as they pass through a component

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what does a greater emf mean

A

more energy per coulomb has been transferred into electrical energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

when is electromotive force used

A

when charged particles ain energy from a source

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the equation for electromotive force

A

E=W/Q
E is emf measured in volts
W is the energy transferred by charge
Q is charge in coulombs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is the work done equation

A

W=VQ or W=EQ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is thermionic emission

A

the emission of electrons through the action of heat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is an electron gun

A

electrical device used to produce a narrow beam of electrons
electrons can be used to ionise particles by adding or removing electrons from atoms
have very precisely determined kinetic energies
used in scientific instruments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

how does an electron gun work

A

need a source of electrons - small metal filament heated by an electric current, electrons in this wire gain kinetic energy
some gain enough kinetic energy to escape from the surface of the metal - thermionic emission
if heated filament is placed in a vacuum and a high pd applied between the filament and an anode the filament acts as a cathode and the freed electrons accelerate towards the anode gaining kinetic energy
if the anode has a small hole in it then electrons in line with this hole can pass through it, creating a beam of electrons with specific kinetic energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what expression relates the work done on the electron to its increase in kinetic energy

A

work done = gain in kinetic energy
eV=1/2mv^2
assumes the electrons have negligible kinetic energy at the cathode

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

why does the work done = the gain in the kinetic energy

A

as electrons accelerate towards the anode they gain kinetic energy
from definition of pd work done on a single electron travelling from the cathode to the anode is equal to eV - e is elementary charge and v is accelerating pd
law of conservation of energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

how can you change the kinetic energy of the electrons within the beam

A

changing the accelerating pd
the greater the pd the more energy is transferred to the electrons and so the faster they move

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is resistance

A

a property of a component calculated by dividing the potential difference across it by the current in it
symbol R
unit ohm
the ratio between the pd and current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is the equation for resistance

A

R=V/I

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what is an ohm

A

the resistance of a component when a pd of 1V is produced per ampere of current
1ohm = 1VA^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is ohms law

A

the potential difference across a conductor is directly proportional to the current in the component as long as its temperature remains constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

how does temperate affect resistance

A

current in the circuit changes because the temp of the wire increases over time as a result of heating caused by the current
as the wire gets hotter its resistance increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
why does when the wire gets hotter the resistance increases
temp of wire increases - positive ions inside wire have more internal energy and vibrate with greater amplitude about mean positions frequency of collisions between the charge carriers and the positive ions increases so the charge carriers so more work, transfer more energy as they travel through the wire
26
what is the current-potential difference characteristics (I-V characteristics)
show the relationship between the electric current I in a component and the potential difference V across it
27
what are the I-V characteristics for a resistor
the potential difference across the resistor is directly proportional to the current in the resistor, as a result - resistor obeys ohms law and so can be described as an ohmic conductor, the resistance of the resistor is always constant the resistor behaves in the same way regardless of the polarity
28
what are the I-V characteristics of a filament lamp
the potential difference across a filament lamp is not directly proportional to the current through the resistor - a filament lamp does not obey ohms law and so can be described as a non-ohmic component, the resistance of the lamp is not constant the filament lamp behaves in the same way regardless of the polarity the resistance of the filament increases as the pd across it increases
29
why is there an increase in resistance in a filament lamp as the pd increases
cause by the wore getting so hot that it glows current increases so does the rate of flow of charge through the filament - more electrons per second pass through it so more collisions occur between the electrons and the positive metal ions per second when electrons collide with ions they transfer energy to ions causing ions to vibrate more or in other words to increase in temp and to collide with still more electrons
30
how do LEDs work
electrical energy is transfers directly into light LEDs do not get hot so they are much more efficient and draw much less power emit light in a single specific wavelength
31
what is a diode
only allows current in one particular direction
32
what are LEDs
light emitting diodes emit light of a single specific wavelength
33
what are the positives about LEDs
efficient take little energy to run
34
what are the I-V characteristics for a diode
the potential difference across a diode is not directly proportional to the current through it - a diode does not obey ohms law and so can be described as a non ohmic component, the resistance of a diode is not consistent the diodes behaviour depends on the polarity
35
what is the threshold pd
the point at which after the diode has very little resistance after this current is able to flow through the diode
36
what are the factors that affect the resistance of a wire
the material of the wire the length of the wire L the cross sectional area of the wire A
37
what is resistivity
a property of a material measured in ohm meters the product of the resistance of a component made of the material and its cross sectional area divided by its length
38
how does length affect resistance
increasing the length of the wire will increase the pd across it doubling the length doubles the pd so the resistance must have doubled resistance of a wire is directly proportional to its length
39
how does cross sectional area affect resistance
when cross sectional area of wire increases the resistance drops greater cross sectional area lower resistance for any given pd doubling the cross sectional area will double the current so the resistance must have halved resistance of wire is inversely proportional to its cross sectional area
40
how do you calculate resistance from resistivity
R is directly proportional to L/A the resistivity (p) of a particular material at a given temperature is the constant of proportionality of this equation P=(pL)/A
41
what is resistivity
resistivity of a material at a given temp is the product of the resistance of a component mad of the material and its cross sectional area divided by the length
42
how does resistivity vary with temp
as the material gets hotter its resistivity increases
43
what experiment can you use to determine resistivity
piece of wire determine the resistivity by how the resistance of the wire varies with its length obtain values for the pd across different lengths of wire current in wire measured to can use R=V/I to calculate the resistance for each length as R directly proportional to L a raph of R against L is a straight line through the origin gradient of the graph is p/A resistivity found by multiplying the gradient of the graph by the cross sectional area of the wire
44
how can you tell if a material is a conductor a semiconductor or an insulator from its resistivity
the small the resistivity the better the conduction e.g. 1.6x10^-8 is a conductor, 7.0x10^17 is an insulator
45
what is a thermistor
a temperature sensing component
46
what are the properties of a thermistor
as the temperature increases the resistance decreases
47
why does as the temp of a thermistor increases does its resistance decrease
negative temperature coefficient number density of charge carriers within the material increases
48
where are thermistors used
in simple thermometers in thermostats to control aircon and heating monitor temp of components in electrical devices
49
what experiment can you do to measure the resistance of a thermistor as it changes with temperature change
using an ohmmeter and a water bath or an ammeter and voltmeter can be used to measure current and pd in a thermistor at different temps, resistance then calculated with R=V/I
50
what are the I-V characteristics of a thermistor
non ohmic current increases the temperature increases temperature increases leads to a drop in resistance because the num density of charge carriers increases increase in temp leads to an increase in the num density of the free electrons
51
what is an LDR
light dependent resistor change resistance depending on the light intensity
52
how does the resistance of an LDR change depending on light
dark - LDR has a very high resistance - num density of free electrons inside the semiconductor is very low light - num density of charge carriers increases - decrease in resistance
53
what experiment can you do to investigate hoe the resistance of an LDR varies with distance from a constant light source
narrow tube placed around LDR will greatly reduce effect of other background sources of light varying the distance from LDR to light source measure the resistance using ohmmeter and distance using meter ruler
54
what are electrical circuits used for
to transfer energy from one place to another e.g. power source to a component that transfers energy into another form whenever there is current in a component energy is transferred from the power source to that component
55
what is the electrical pwer
the rate of energy transfer by each electrical component
56
what does electrical power depend on
current in the component and the pd across it
57
what is the equation for electrical power
electrical power = current x pd P=IV
58
what power equations can you make from P=IV and V=IR
P=IV P=(IR)I P=I^2R I=V/R P=(V/R)V P=V^2/R
59
how do you derive the equation P=IV
P=W/t V=W/Q W=V/Q P=(VQ)/t Q/t=I P=IV
60
how can you calculate the energy transferred using P=IV
equation for electrical power P=W/t rearranged to get W=Pt sub in P=IV W=VIt W in energy transferred in joules V is pd in volts I is current in amps t is time in second
61
how is the amount of energy used in a house measured
electricity meter records the transfer of energy from national grid to the house
62
what is the equation for power
power=energy transferred/time taken P=W/t
63
what is the equation for energy transferred by an electrical device
rearrange the power equation to get W=Pt
64
what is the kilowatt-hour
very large unit of energy the energy transferred by a device with a power of 1kW operating for a time of 1hour 1KW = 3.6MJ
65
what is the equation for energy transferred when using the units kWh
energy transferred = power of device (kW) x time for which the device is used (h)

physics module 4 - electrons, waves and photons (3 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions