A level Physics A OCR Paper 2
Study
What is elementary charge equal to?
1.6 x10^-19 C
What direction does convectional current travel?
From + to -
What direction is electron flow?
From - to +
State Kirchhoff's first law
At any point in an electrical circuit, the sum of currents entering a point is equal to the
sum of currents leaving the point
What is mean drift velocity?
The average velocity of electrons as they move through a wire
Difference between conductors, semiconductors and insulators
Conductors - High number density
Semiconductors - Medium number density
Insulator - Low number density
What are the circuit symbols?
Definition of p.d
Energy transferred from electrical energy to other forms per unit charge
Definition of e.m.f
Energy transferred from chemical to electrical energy per unit charge
Difference between p.d and e.m.f
p.d - work done BY the charge carriers
e.m.f - work done ON the charge carriers
How does an Electron gun work? Briefly or image
1) Metal filament in vacuum is heated by current
2) Electrons gain KE, some gain enough to escape surface of metal (thermionic
emission)
3) Electron passes through anode with hole in it, creating a beam
State Ohm's Law
The p.d across a conductor is directly proportional to the current in the component as
long as the temp is constant
Temp and resistance
As temp increases, +ve ions vibrate more due to increases internal energy, increasing
collisions with electrons, causing more work needed to travel though wire
I-V characteristics for a Resistor
Obeys Ohm's Law
Lower resistance = steeper gradient
I-V characteristics for a Filament Lamp
Doesn't obey Ohm's Law
I-V characteristics for Diode
Circuit for collecting data for an I-V characteristic
Take values for I and V, plot on I-V graph
What are the 2 thermistor types? What is the I-V characteristic for them
, Negative Temp Coefficient (NTC)
Positive Temp Coefficient (PTC)
State the term Resistivity
A property of a material in Ω m, defined as the product of the resistance of a component
of the material and its cross-sectional area divided by its length
Determining Resistivity
Measure diameter to work out area. Calc resistance from V and A
Plot resistance against length graph. Find gradient and multiply by area to find resistivity
Kilowatt-hour (kWh)
1 kWh = 3.6MJ
Kirchoff's Second Law
In a closed loop of an electrical current, the sum of the e.m.f.s is equal to the sum of
p.d.s
Current in series and parallel circuits
Current acts like water currents
Series - same in all places
Parallel - splits at each branch
Voltage in series and parallel circuits
Series - splits at each component
Parallel - same at each branch
Combining resistors in series and parallel circuits
Series - R = R1 + R2 + ...
Parallel - 1/R = 1/R1 + 1/R2 + ...
What is internal resistance?
The resistance inside the battery/cell/power supply caused by the electrons (moved by
the chemical energy) colliding with atoms inside the device.
This resistance causes a loss of volts, call lost volts
Relationship between e.m.f, terminal p.d and lost volts
e.m.f = terminal p.d + lost volts
Investigating Internal Resistance
Plot a graph of V against I
y = mx + c and V =-rI + e.m.f
y=V
gradient = r
x=I
Find gradient for resistivity
What is a potential divider?
An electrical circuit designed to divide the p.d across 2 or more components in order to
produce a specific amount of output
Transvers waves vs Longitudinal Waves
Transverse - Oscillations perpendicular to direction of energy transfer
Longitudinal - Oscillations parallel to transfer of energy transfer
Reflection and Refraction
Reflection - it is what it is...
Angle of incident = Angle of reflection
Study
What is elementary charge equal to?
1.6 x10^-19 C
What direction does convectional current travel?
From + to -
What direction is electron flow?
From - to +
State Kirchhoff's first law
At any point in an electrical circuit, the sum of currents entering a point is equal to the
sum of currents leaving the point
What is mean drift velocity?
The average velocity of electrons as they move through a wire
Difference between conductors, semiconductors and insulators
Conductors - High number density
Semiconductors - Medium number density
Insulator - Low number density
What are the circuit symbols?
Definition of p.d
Energy transferred from electrical energy to other forms per unit charge
Definition of e.m.f
Energy transferred from chemical to electrical energy per unit charge
Difference between p.d and e.m.f
p.d - work done BY the charge carriers
e.m.f - work done ON the charge carriers
How does an Electron gun work? Briefly or image
1) Metal filament in vacuum is heated by current
2) Electrons gain KE, some gain enough to escape surface of metal (thermionic
emission)
3) Electron passes through anode with hole in it, creating a beam
State Ohm's Law
The p.d across a conductor is directly proportional to the current in the component as
long as the temp is constant
Temp and resistance
As temp increases, +ve ions vibrate more due to increases internal energy, increasing
collisions with electrons, causing more work needed to travel though wire
I-V characteristics for a Resistor
Obeys Ohm's Law
Lower resistance = steeper gradient
I-V characteristics for a Filament Lamp
Doesn't obey Ohm's Law
I-V characteristics for Diode
Circuit for collecting data for an I-V characteristic
Take values for I and V, plot on I-V graph
What are the 2 thermistor types? What is the I-V characteristic for them
, Negative Temp Coefficient (NTC)
Positive Temp Coefficient (PTC)
State the term Resistivity
A property of a material in Ω m, defined as the product of the resistance of a component
of the material and its cross-sectional area divided by its length
Determining Resistivity
Measure diameter to work out area. Calc resistance from V and A
Plot resistance against length graph. Find gradient and multiply by area to find resistivity
Kilowatt-hour (kWh)
1 kWh = 3.6MJ
Kirchoff's Second Law
In a closed loop of an electrical current, the sum of the e.m.f.s is equal to the sum of
p.d.s
Current in series and parallel circuits
Current acts like water currents
Series - same in all places
Parallel - splits at each branch
Voltage in series and parallel circuits
Series - splits at each component
Parallel - same at each branch
Combining resistors in series and parallel circuits
Series - R = R1 + R2 + ...
Parallel - 1/R = 1/R1 + 1/R2 + ...
What is internal resistance?
The resistance inside the battery/cell/power supply caused by the electrons (moved by
the chemical energy) colliding with atoms inside the device.
This resistance causes a loss of volts, call lost volts
Relationship between e.m.f, terminal p.d and lost volts
e.m.f = terminal p.d + lost volts
Investigating Internal Resistance
Plot a graph of V against I
y = mx + c and V =-rI + e.m.f
y=V
gradient = r
x=I
Find gradient for resistivity
What is a potential divider?
An electrical circuit designed to divide the p.d across 2 or more components in order to
produce a specific amount of output
Transvers waves vs Longitudinal Waves
Transverse - Oscillations perpendicular to direction of energy transfer
Longitudinal - Oscillations parallel to transfer of energy transfer
Reflection and Refraction
Reflection - it is what it is...
Angle of incident = Angle of reflection
