# IB Physics definitions

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Instantaneous speed
The speed of an object at a particular instant in time.
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Average speed
The distance travelled divided by the time taken.
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Weight
The force on an object due to gravity.
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Newton's 1st Law of Motion
An object with no resultant force acting on it, will travel at a constant speed in a straight line (or remain at rest)
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Newton's second law
F = change in momentum/time (unbalanced force is given by rate of change of momentum)
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Newton's third law
For every force there is an equal and opposite force
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Translational equilibrium
The resultant force acting on the object = 0
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The law of conservation of momentum
The total momentum in any direction, of an isolated system will remain constant
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The law of conservation of total energy
For an isolated system the total energy of the system is a constant value
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Power
The work done in 1 second
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Elastic collision
A collision where the total kinetic energy is conserved
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Frequency
The number of waves per second
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Period
The time taken for one complete wave cycle
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Wavefront
A line of constant phase.
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Damping
The decay of vibrational energy as a result of a force acting in opposition to the motion of the particles
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Intensity
Energy per unit area per unit time
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Refractive index
The speed of light in a vacuum/speed of light in object
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Standing waves
Waves that do not transmit energy
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Progressive wave
Waves that do transmit energy
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Constructive interference
Waves that have a phase difference of 0 degrees. The interference produces that maximum possible displacement.
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Destructive interference
Waves that have a phase difference of 180 degrees. The interference produces the minimum possible displacement
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The Principle of Superposition
Waves of the same type, in the same space at the same time overlap, the displacement is the sum of the displacement of each wave
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Electrical potential difference
The change in the electric potential energy per unit charge when moving a test charge from one point to another.
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The electron volt
The energy gained of lost by an electron when it moves through a voltage of 1V.
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Resistance
The opposition to a flow of current.
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Electromotive force
The energy per unit charge converted into other form from a battery of power supply.
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Gravitational field strength
The gravitational force per unit mass/ the gravitational flux per unit area
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Electric field strength
The electric force per unit charge/the electric flux per unit area
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Magnitude of a magnetic field
The magnetic flux per unit area.
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Unified atomic mass unit
1/12 of the mass of a C-12 atom
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Mass defect
The amount that the total mass of the nucleus is less than the total mass of the nucleus's constituent particles
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Binding energy
The energy required in splitting up the nucleons from the nucleus of an atom
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Energy density of a fuel
The energy stored in a fuel per unit volume
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Albedo
The ratio of light reflected by a planet to the light received by it
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Coefficient of volume expansion
The fractional change in volume as a result of a temperature change of 1K
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Electric potential
The energy per unit charge in moving a test charge from infinity to a given point
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Electric potential energy
The energy needed to move a charge from one point to another
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Gravitational potential
The energy to bring a unit point mass from infinity to a given point
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Gravitational potential energy
The energy needs to bring a point mass from one point to another
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Magnetic flux
A measure of the magnetic fields strength - the total number of magnetic lines of force passing through a specified area in a magnetic field.
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Magnetic flux * The number of turns for a coil
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The probability of a decay of a nucleus per unit time
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Capacitance
The stored charge per unit volt
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Quantum efficiency
The ratio of the number of photoelectrons emitted to the number of photons incident of the pixel
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Magnification
The ratio of the length of the image on the CCD to the actual length of the object
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CCD
A charged couple device (each pixel is converted to an electric charge the intensity of which is related to a colour in the colour spectrum)
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Light year
The DISTANCE traveled by light in one year. (9.4605284 × 10^15 metres)
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Luminosity
The total energy per second given out by an object
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Parsec
The distance an object would be if it had a HELIOCENTRIC PARALLAX of 1 second or an arc
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Absolute magnitude
The magnitude of a star as seen from a distance of 1 parsec
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Critical density
The density of the universe which would halt its expansion at infinite time.
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Principle axis
A line that passes through the centre of curvature of a lens so that light is neither reflected nor refracted
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Focal lens (of a convex lens)
The distance over which the lens will focus plane waves
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Linear magnification (of a convex lens)
The ratio of the image size to the object size
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Power (of a convex lens)
The curvature a lens adds to plane waves. Given by one over the focal length.
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The Dioptre
Unit for measuring curvature by: 1/distance from source of waves
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Far point
The largest distance for which a relaxed eye can focus light onto the retina. For normal vision this is taken as infinity.
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Near point
The closest point an object can be to the eye and still be focuses without strain. For normal vision this is taken at about 25cm
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Angular momentum
The product of the momentum of an object and the perpendicular distance from the axis of rotation.
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## Other cards in this set

### Card 2

#### Front

The distance travelled divided by the time taken.

Average speed

### Card 3

#### Front

The force on an object due to gravity.

### Card 4

#### Front

An object with no resultant force acting on it, will travel at a constant speed in a straight line (or remain at rest)

### Card 5

#### Front

F = change in momentum/time (unbalanced force is given by rate of change of momentum)