Definitions Flashcards
converging lens
a type of lens which is designed to cause rays to converge towards one another
diverging lens
a type of lens which is designed to cause rays to diverge away from one another
ionisation
the process whereby an atom gains or loses an electron
absorbed dose
When ionising radiation passes through an absorbing medium (e.g. the human body) its nuclear energy is deposited in the absorbing tissue. This is measured by the absorbed dose which is the energy absorbed per unit mass of the absorbing material.
nuclear fission
Nuclear fission takes place when a neutron collides with a large unstable nucleus which is large in mass. This causes it to split into two smaller massed nuclei. At the same time it releases more neutrons and a lot of heat energy.
nuclear fusion
Nuclear fusion takes place when two small nuclei of small mass collide and join to create a larger massed nucleus. At the same time a lot of heat energy is released.
chain reaction
Neutrons go on to produce further fission reactions.
fuel rods
Made of uranium-238 enriched with uranium-235 which produces energy by nuclear fission.
moderator
The moderator, graphite, has the fuel rods embedded in it. It slows down neutrons that are produced in fission, since a nucleus is split more easily by slow moving neutrons.
control rods
The boron control rods control the rate of production of energy. The boron rods absorb neutrons so by lowering them into the reactor, the reaction can be slowed down. In the event of an emergency they are pushed right into the core of the reactor and the chain reaction stops completely.
coolant
A cooling system is needed to cool the reactor and to transfer heat to the boilers in order to generate electricity. British gas-cooled reactors use CO2 as a coolant.
containment vessel
Its made of thick concrete which acts as a shield to absorb neutrons and other radiation
wave
transfers energy from one place to another
transverse waves
a wave where its particles move perpendicular to the direction of travel. can travel through both a medium and a vacuum
longitudinal waves
a wave where its particles move parallel to the direction of travel. can travel through a medium only, not a vacuum.
amplitude
vertical distance from the equilibrium position to either the crest or trough.
frequency
number of waves per second that passes a particular point
period
time taken for one complete wave to pass a particular point.
diffraction
the effect of waves bending when they meet obstacles
ultrasound
has a higher frequency than 20,00Hz and cannot be heard by humans.
normal
a dotted line that exists at 90* to the boundary between two different mediums where the wave enters the boundary.
angle of incidence
the angle between the normal and the incident ray
angle of reflection
the angle between the normal and the reflected ray
angle of refraction
the angle between the normal and the refracted ray.
critical angle
the angle of incidence that produces an angle of refraction of 90*
reflection
the deflection of a wave without any absorption of it taking place.
refraction
the process whereby a wave experiences a change in speed and hence direction when it crosses a boundary between two different mediums at an angle of incidence that is greater than zero.
dispersion
the process whereby white light is separated into its component colours though the use of a lens.
total internal reflection
the process whereby the angle of incidence of a wave exceeds the critical angle and the wave is reflected within the medium it enters without crossing the boundary to a second medium and exiting it as a consequence.
lenses
an object made of transparent material which is designed to refract waves
scalar
a physical quantity that possesses a magnitude and unit only.
vector
a physical quantity that possesses a direction, magnitude and unit.
velocity
the rate of change in displacement
speed
the rate of change in distance
displacement
the straight line distance from the start to finish points.
resultant
the equivalent to the combined effect of two or more component vectors acting at the same point.
acceleration
the rate of change in velocity
force
the interaction between objects that causes them to change speed, direction and/or shape.
Newton’s First Law of Motion
An object will continue to travel at a constant speed in a straight line unless it is acted upon by an unbalanced force.
Newton’s Second Law of Motion
The acceleration of an object is directly proportional to the magnitude of the unbalanced force acting upon it and is inversely proportional to its mass.
Newton’s Third Law of Motion
If object A exerts a force on object B, then object B will exert an equal but opposite force on object A. (every action has an equal but opposite reaction)
balanced forces
Forces that act in opposite directions but are equal in magnitude. The resultant force is 0 N.
unbalanced force
forces are not balanced and so the resultant force is non zero.
friction
a force that opposes the direction of movement of an object.
weight
the force exerted on an object by the pull of gravity of Earth.
mass
the amount of matter contained within an object
gravitational field strength
the ratio of weight to mass
projectile motion
An object will exhibit this when it is travelling horizontally and vertically at the same time. The object travels at a constant velocity horizontally and accelerates uniformly vertically.
light year
the distance light travels in one year.
1 ly = 9.5 x 10^15 m
geostationary satellite
a satellite that is positioned above a point on the Earth’s surface. Its period of orbit is equal to Earths.
continuous spectrum
a spectrum that contains a continuum of visible wavelengths
line spectra
a bright line formed as part of an emission or absorption spectrum.
current
the electrical current electric charge transferred per unit time.
alternating current (a.c.)
the current constantly changes its value and changes direction at regular time intervals flowing first one way then the other.
direct current (d.c.)
a continuous current flowing in only one direction.
potential difference (voltage)
it is a measure of the energy given to the electrons. The potential difference of a supply is a measure of the energy given to the electrical charge carriers in a circuit.
resistance
the opposition of a conductor in a circuit to the flow of a current through that conductor in a circuit
ohm’s law states that
the current flowing through a conductor is directly proportional to the potential difference (voltage) across it at a constant temperature within the conductor itself.
series circuit
where the current only has one path to flow through and follow
parallel circuit
where the current has more than one path to flow through and follow. there is at least one point in the circuit where there is a choice of paths.
electronic system
a series of electronic parts connected together to perform a particular function.
input device
an electrical component which transforms one form of energy into electrical energy
process device
an electrical component which transforms the electrical signal received from the input device into a useable form and transmits it to the output device
output device
an electrical component which transforms electrical energy into another form of energy
potential (voltage) divider
They are used to split a potential difference. They are a device or circuit that uses two or more resistors / a variable resistor to provide a fraction of the available voltage from the supply. The supply voltage is divided across the resistors in direct proportion to their individual resistances. The p.d. across any single resistor depends upon what proportion its resistance is of the total resistance of the circuit.
transistor
Can be used as an electronic switch. A transistor has three connections called the emitter base and collector.
threshold voltage
By applying a p.d. between the base and emitter, the transistor can be made to conduct through the emitter and collector. The p.d. required to switch on the transistor (the threshold voltage) is 0.7 V or above.
power
the rate at which appliances transform energy is defined as electrical power.
energy
a measure of the ability of a system to do work
law of conservation of energy
states that energy cannot be created or destroyed only transformed from one form into another or transferred from one object to another. The total amount of energy remains constant during energy transfers.
efficiency
is a measure of the proportion of the total input energy that is transformed into useful output energy
work done
a measure of energy transformed.
gravitational potential energy
a measure of work done against gravity
kinetic energy
The energy associated with a moving object. The kinetic energy of a moving object depends upon the mass of the object and on the square of its speed.
temperature
a measure of how hot or cold and object is and is defined as the mean kinetic energy of its particles - the greater the temperature of an object the greater kinetic energy the particles will gave.
heat energy
A form of energy transferred between objects at different temperatures. The greater the temperature difference between objects, the greater the rate of transfer of energy will take place.
specific heat capacity
the amount of heat energy required to change the temperature of a mass of one kilogram by one degree Celsius.
specific latent heat
the amount of heat energy that is required to change the state of a mass of one kilogram at either its melting or boiling point at the same temperature depending upon the change of state that is occurring.
specific latent heat of fusion
the heat energy required to change a mass of one kilogram of substance from a solid at its melting point to a liquid at the same temperature.
specific latent heat of vaporisation
the heat energy required to change a mass of one kilogram of substance from a liquid at its boiling point to a gas at the same temperature.
pressure
It is caused by the particles of gas colliding with a boundary such as a container wall. It is also caused by a force pushing against something.
absolute zero
the temperature at which gas particles cease to move, have zero kinetic energy and so exerts no pressure.
kelvin scale of temperature
a division on the kelvin temperature scale is the same magnitude as one division on the Celsius temperature scale so temperature differences as the same in Kelvin as in Celsius. A 1*C change is the same as a 1 K change.
N (when referring to waves)
number of waves contained within a distance
