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Summary A Level Physics Notes
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Highly detailed A-level physics notes, going over each and every topic taught in the new A-level physics syllabus. Notes include formulas and learning objectives.
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1PHYSICS
12 MOTION IN A CIRCLE
12.1 KINEMATICS OF UNIFORM CIRCULAR MOTION
Define the radian and express angular displacement in radians.
Understand and use the concept of angular speed.
Recall and use ω = 2π/ T and v = rω.
» A radian is the angle subtended at the centre of the circle when the arc is equal in length
to the radius.
» Angular displacement in the displacement covered of a circle:
s = θr Displacement = Angular Displacement * Radius
» Angular speed:
2π 2π
ω= Angular Speed=
T Period
ω=2 πf Angular Speed = 2 π∗Frequency
» Velocity:
v = rω Velocity = Radius * Angular speed
12.2 CENTRIPETAL ACCERLERATION
Understand that a force of constant magnitude that is always perpendicular to the direction of motion causes
centripetal acceleration.
Understand that centripetal acceleration causes circular motion with a constant angular speed.
Recall and use a = rω2 and a = v2/r.
Recall and use F = mrω2 and F = mv2 /r.
» The time taken to complete one rotation is called the time period.
» For an object to move in a circular path, a centripetal force needs to be maintained.
» The resultant force acting towards the centre of a circle in line with the radius is called the
centripetal force.
» Centripetal doesn’t change the magnitude of the object’s velocity and the object’s velocity
is always along a tangent to the circle, but the magnitude of centripetal force is constant.
» Centripetal force acts perpendicular to the object’s movement, along the radius of the
circle.
» Centripetal acceleration is caused by centripetal force of constant magnitude which is
always perpendicular to the direction of motion.
» The force acting towards the centre (centripetal force) pushes the object at right angle to
the direction of motion, this causes the object to spin in circular at constant magnitude of
velocity, meaning centripetal force and centripetal acceleration causes circular motion and
since magnitude of velocity doesn’t change, angular speed is also constant.
» Acceleration:
a = rω2 Acceleration = Radius * (Angular Speed)2
a = v /r
2
Acceleration = (Velocity)2 / Radius
, 2
» Centripetal force:
F = mrω2 Force = Mass * Radius * (Angular Speed) 2
F = mv2 /r Force = (Mass * (Velocity)2) / Radius
13 GRAVITATIONAL FIELDS
13.1 GRAVITATIONAL FIELDS
Understand that a gravitational field is an example of a field of force and define gravitational field as force per
unit mass.
Represent a gravitational field by means of field lines.
» A gravitational field is a field of force with non-contact interactions.
» Objects placed in a gravitational field experience a force.
» Gravitational field at a point is the gravitational force per unit mass.
» Gravitational field is a vector quantity.
» Fields line are used to represent gravitational fields, the fields lines are labelled with arrows
to show the field’s direction.
» Gravitational field strength is equal to the acceleration of free fall.
» g = F/m Gravitational field strength = Gravitational force/ mass
13.2 GRAVITATIONAL FORCE BETWEEN POINT MASSES
Understand that, for a point outside a uniform sphere, the mass of the sphere may be considered to be a point
mass at its centre.
Recall and use Newton’s law of gravitation F = Gm1 m2/r 2 for the force between two point masses.
Analyse circular orbits in gravitational fields by relating the gravitational force to the centripetal acceleration it
causes.
Understand that a satellite in a geostationary orbit remains at the same point above the Earth’s surface, with
an orbital period of 24 hours, orbiting from west to east, directly above the Equator.
» A mass that isn’t a uniform sphere can be consider as a point mass, where the point mass
is at its centre.
» Inverse square law:
Gravitational field strength decrease with distance.
If distance is doubles, gravitational field strength is decreased by a factor of 4.
Gravitational field strength ∝ 1/distance2.
» Newton’s Law of Gravitation:
Any two point masses attract each other with a force that is directly proportional to
the product of their masses and inversely proportional to the square of the
distance between their centre.
A sphere of uniform density can be treated mathematically as having all of its mass
concentrated at a point at its centre and can therefore be described as a point
mass.
Any two masses in each other’s gravitational field would exert a force on each
other.
F = Gm1m2/ r2 Force between point masses = Gravitational constant * mass 1 *
mass 2 / radius2
Radius in the force between point masses equation is the distance between the
centres of the two point masses.
» To maintain a constant height above Earth, an object must have a specific orbital speed.
» If an object moves too fasts above Earth, it will go further into space.
» If an object moves too slow above Earth, it will fall to Earth.
, 3
» For an object spinning around Earth, that object gains in centripetal force/acceleration from
the gravitational field of Earth.
» A geostationary orbits means an object that remains at the same point above Earth, in
order to achieve this the object must have an orbital period of 24 hours, orbit form east to
west, and orbit above the Equator.
13.3 GRAVITATIONAL FIELD OF A POINT MASS
Derive, from Newton’s law of gravitation and the definition of gravitational field, the equation g = GM/r 2 for the
gravitational field strength due to a point mass
Recall and use g = GM/r2
Understand why g is approximately constant for small changes in height near the Earth’s surface
» g = GM/r2 Gravitational field strength of point mass = Gravitational constant * mass/
radius 2
» The above equation can be derived from by equating g = GM/r 2 and F = mg together.
» For small changes in height near the Earth’s surface, the value of g can be consider to be
constant, meaning near the Earth’s surface there is a uniform gravitational field, this
because the field lines are almost parallel and equidistance.
13.4 GRAVITATIONAL POTENTIAL
Define gravitational potential at a point as the work done per unit mass in bringing a small test mass from
infinite to the point.
Use Φ = –GM/r for the gravitational potential in the field due to a point mass.
Understand how the concept of gravitational potential leads to the gravitational potential energy of two point
masses and use EP = –GMm/r
» When an object moves so far away that it is unaffected by Earth’s gravity, this point is
called infinity.
» At infinity gravitational potential energy is at its maximum.
» Gravitational potential:
Represented by the symbol Φ.
Work done per unit mass in bringing a small test mass from infinity to a point in a
field.
Gravitational potential is negative as work is being done against the point to get it
away from infinity.
Scalar quantity.
Φ = -GM/r Gravitational potential = -(Gravitational constant * Mass)/distance
from mass and point
» Gravitational potential energy of E of a system of two points mass is:
EP = -GMm/r = Gravitational potential energy = -(Gravitational constant * Mass 1 *
Mass 2)/radius
14 TEMPERATURE
14.1 THERMAL EQUILIBRIUM
Understand that (thermal) energy is transferred from a region of higher temperature to a region of lower
temperature.
Understand that regions of equal temperature are in thermal equilibrium.
» When two objects are in contact, they are said to be thermal contact because thermal
energy can be transferred between them.
» Thermal energy is transferred from regions of higher temperature to regions of lower
temperature through conduction and convection.
, 4
» Thermal energy lost by the region of high temperature is the thermal energy gained by the
region of lower temperature.
» When the temperature of two substances are equal meaning there won’t be anymore net
transfer of energy, they are said to be in thermal equilibrium.
» Thermal energy is total kinetic energy of all the particles of a substance.
» Temperature and thermal energy are not equivalent.
14.2 TEMPERATURE SCALES
Understand that a physical property that varies with temperature may be used for measurement of
temperature and state examples of such properties, including the density of a liquid, volume of a gas at
constant pressure, resistance of a metal, emf of a thermocouple.
Understand that the scale of thermodynamic temperature does not depend on the property of any particular
substance.
Convert temperature between kelvin and degrees Celsius and recall that T/K = θ / OC + 273.15.
Understand that the lowest possible temperature is zero kelvin on the thermodynamic temperature scale and
that this is known as absolute zero.
» Thermometers are a device used to measure the temperature of a substance.
» There are many different types of thermometers that utilise different temperature-
dependant physical properties of substances.
» Density of a liquid thermometer.
Liquid in glass thermometer.
The liquid is stored in a narrow tube, as the liquid is heated up the liquid expands
or contracts and rises or falls, the temperature scale is printed on the glass.
Examples of liquid: Ethanol, mercury.
The liquid in the glass determines the useful temperature range.
Portable and easy to use.
Lack accuracy and have small useful temperature ranges.
» Volume of a gas at constant pressure thermometer:
Gas thermometers or constant pressure gas thermometer.
When gas pressure is kept constant, volume of gas varies linearly with
temperature.
As the temperature of the gas in the spherical bulb increases/decreases, the
volume increases/decreases, the liquid inside the gas thermometers then
rises/falls, the change in position of the liquid can be used to determined change in
volume, and so temperature change.
Rather used to calibrate other thermometers then as thermometers themselves.
Accurate to ±5 x 10-3 OC, and can be used to measure temperature over ranges
such as -200 to 500 OC.
Large and fragile.
If high level of accuracy is needed, you need to take into account atmospheric
pressure.
» Resistance of a metal thermometer:
Electrical resistance of metal increases with temperature.
Platinum’s change in resistance with temperature is almost linear, so they are used
as platinum resistance thermometers.
They are very sensitive, able to detect temperature changes of the order of 10 -3 OC.
They are usually very small, so they can be installed in confined spaces.
Able to be connect to other devices such as digital displays.
Thermistors:
o Give rapid responses to temperature change.
o Sensitive.
o Resistance changes a lot with small change in temperature.
o Resistance does not change uniformly, so thermistors are difficult when it
comes to calibrating an accurate scale.
» Thermocouple:
Used thermoelectric effect to measure temperature.
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