Physics Definitions

refraction

The bending of light as it goes from one medium to another.

Cathode Rays

Streams of high speed electrons moving from the cathode

The Weber

magnetic flux density over an area of 1m² is 1 Tesla, then the flux through the area is 1 ____

Ohm

1 ampp through the Pd across it is 1 volt in a conductor

Ion

A molecule or atom that has lost or gained one or more electrons

Kilowatt-Hour

The amount of energy used by 1000 W appliance in 1 hour

Forward Biased

Conducts current

Reverse-Bias

Doesnt conduct current

Light

Light is a form of energy that travels at 3×10^8 m/s

Laws of Refraction

(1) Incident ray, refracted ray & normal are on the same plane.  (2) Sine I/Sine R is constant.

Refractive Index

Sine I/Sine R = 1/Sin C = Real depth/Apparent depth = c1/c2.

The ratio of the sine of the angle of incidence to the sine of the angle of refraction when light travels from a vacuum into that medium.

Real Image

Image formed by the actual intersection of light rays.

Virtual Image

an image formed by the apparent intersection of light rays

Magnification

the ratio of the height of the image to the height of the object, indicating how much larger or smaller the image is compared to the object.

m = v/u

Parallax

The apparent movement of one object relative to another.

Critical Angle

The angle whose angle of incidence is 90 when light goes from a denser to a rarer medium.

Total Internal Reflection

• When light travelling from a denser to a rarer medium strikes the second medium with an angle of incidence greater than the critical angle, it is reflected back.

Optical fibre

A thin transparent rod, through which light can travel by total internal reflection.

Converging lens (convex)

A lens that brings parallel rays of light to a single point or focus.

Diverging lens (concave)

A lens that spreads parallel rays of light outward, causing them to appear to diverge from a single point or focus.

Scalar Quantity

A physical quantity that has only magnitude and no direction, such as mass or temperature.

Vector quantity

A physical quantity that has both magnitude and direction, such as velocity or force.

Force

Anything that causes the velocity of an object to change.

Joule

One joule is the work done when a force of 1 newton acts for a distance of 1 metre in the direction of the force.

Acceleration

• the rate of change of velocity per unit time.

Power (of a lens)

The ability of a lens to converge or diverge light rays, defined as the inverse of its focal length.

p = 1/f

Speed

The rate of change of distance with respect to time

Displacement

Distance in a given direction

Velocity

Rate of change of displacement with respect to time

Constant Velocity

Velocity that does not change over time, moving in a straight line at a uniform speed.

The Newton

The force that gives a mass of 1kg an acceleration of 1m/s²

Mass

The measure of how difficult it is to accelerate that body

Weight

The force of the earths gravity acting on it

W = MG

Newton's first law of motion?

A body will remain in a state of rest or travelling at a constant velocity unless an external force acts on it.

Newton's second law of motion.

when an unbalanced force acts on a body the rate of change of the body’s momentum is directly proportional to the force and takes place in the direction of the force.

Newtons third law of motion

If body A exerts a force on body B, body B exerts an equal but opposite force onto body A.

Momentum

Mass x Velocity

The principle of conservation of momentum

states that the total momentum of a closed system remains constant if no external forces act on it.

Density

Of a substance is mass per unit volume

Pressure

force per unit area. P = F/A -> Due to liquid: P = pgh

Equilibrium

Vector sum of forces is zero
sum of moments is zero

Archimedes’ Principle

when an object is partially or completely immersed in a fluid it experiences an upthrust equal in magnitude to the weight of the fluid displaced.

Law of Flotation

The weight of a floating body is equal to the weight of the fluid it displaces.

Boyle’s law

• at constant temperature the volume of a fixed mass of gas is inversely proportional to to its pressure.

Newton’s Law of Universal Gravitation

• any two point masses in the universe 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 them.

Moment

Force x Perpendicular distance.

Couple 

Two parallel forces with the same magnitude acting in opposite directions.

Torque

the moment of a couple, T = FD

Work

Force x Displacement.

When force F moves a body through a displacement S in the direction of the force, the work W is equal to the force multiplied by the displacement,

Energy

the ability to do work.

Principle of Conservation of Energy

Energy cannot be created or destroyed but can only be converted from one form to another.

Ek

1/2mv².

The energy that a object possesses due to its motion, where m is mass and v is velocity.

Ep

mgh

the energy it has due to its position in a force field

Power

• Work done ÷Time taken || P = w ÷ t (Watt = Joule/Second)

The rate at which work is done OR the rate at which energy is converted from one form to another

Percentage efficiency

Efficiency = (Useful output energy ÷ Total input energy) × 100%.

Angular Velocity

The rate of change of angle per unit time.

Centripetal Force

• If a body is moving in a circle, the force towards the centre needed to keep it moving is centripetal force.

Centripetal Acceleration

The acceleration of an object moving in a circular path, directed towards the center of the circle.

Period of an Orbit

The time taken for an object to complete one full orbit around a central body.

simple harmonic motion

1. Acceleration is directly proportional to the distance from a fixed point and directed towards that point.

2. its acceleration is always directed towards that point

Hooke’s law

When an object is bent, stretched or compressed by a displacement “s”, The restoring force is directly proportional to the displacement, provided the elastic limit is not exceeded.

Temperature

The hotness or coldness of a body.

Thermometric properties

• any physical properties that change measurably with temperature.

Specific Heat Capacity

• the heat energy needed to change the temperature of 1kg of the substance by 1K. (J/kg/K)

Latent heat

the heat energy needed to change its state without a change in temperature.

Specific Latent Heat

(of fusion) - to liquid
(of vaporisation) - to gas

• the amount of heat energy needed to change the state of 1kg of that substance without changing its temperature. (J/kg)

Conduction

the movement of heat energy through a substance by the passing on of molecular vibration from molecule to molecule. There is no overall motion of the substance

Convection

The transfer of heat through a fluid by means of circulating currents caused by the heat.

Radiation

• the transfer of heat energy from one place to another in the form of electromagnetic waves.

U Value

• the amount of heat energy lost per second through 1m2 of the structure when a temperature difference of 1K is maintained between its ends.

Solar Constant

• the average amount of the sun’s energy falling per second perpendicularly on 1 m2 of the earth’s atmosphere. 1.35 kW/m2

Travelling mechanical wave

A disturbance carrying energy through a medium without any overall motion of that medium

Travelling Wave

either mechanical or electromagnetic, is a disturbance that travels out from the source producing it, transferring energy from the source to other places through which is passes

Transverse wave

A wave where the direction of the wave is perpendicular to the direction of vibration.

Longitudinal wave

A wave where the direction of the wave is parallel to the direction of vibration.

Reflection

The bouncing of waves off an obstacle in their path.

Refraction

• the changing of direction of a wave as it enters a region where its speed is different.

Diffraction

• is the sideways spreading of waves into the region beyond a gap or around an obstacle.

Interference

• When two waves from two sources meet, a new wave is produced. The displacement produced at any point by this wave is the algebraic sum of the displacements that each wave would produce on its own. This is called interference of waves.

Constructive interference

• When waves from two sources meet and the amplitude of the resulting wave is greater than the amplitudes of the individual waves.

Destructive Interference

• When waves from two sources meet and the amplitude of the resulting wave is less than the amplitude of the individual waves.

Coherent Sources

• Two sources of waves are said to be coherent if they are in phase or if there is a constant phase difference between waves from each of the sources. If this is so, the sources must also have the same frequency.

Interference Pattern

• is the resulting pattern when waves from two or more coherent sources meet.

Stationary wave

• When two periodic travelling waves of the same frequency and amplitude moving in opposite directions meet, they interfere with each other. The resulting wave is a stationary wave or a standing wave.

Doppler effect

The apparent change in frequency of waves due to the motion of the source or the observer.

Frequency

of a vibration is the number of cycles occurring per second.

Overtones

• are multiples of the fundamental frequency.

Characteristics

Loudness = Amplitude

Pitch = Frequency

Quality = Number of overtones present in the note and the relative strength of each overtone present

Harmonics

Multiples of a certain frequency f.

F = first harmonic
2F = second etc.

Frequency limits of Audibility

• are the highest and lowest frequencies that can be heard by the human ear. 20Hz – 20kHz.

Resonance

• If the frequency of a periodic force applied to a body is the same as or very near to its natural frequency that body will vibrate with very large amplitude. This phenomenon is called resonance.

Sound Intensity

• The rate at which sound energy is passing through unit area at right angles to the direction in which the sound is travelling at that point. I = P/A (W/m2)

Threshold of Hearing

• is the smallest sound intensity detectable by the average human ear at a frequency of 1kHz. 1 x 10-12W/m2.

The grating constant

The distance d between 2 adjacent slits. (width of 1 line and 1 slit)

Dispersion

The separating of the different wavelengths (colours) present in light

Secondary colour

A colour produced by mixing two primary colours of light, resulting in colours such as cyan, magenta, and yellow.

Complementary colour

A colour that, when combined with a given primary colour of light, results in white light. Examples include red for cyan, green for magenta, and blue for yellow.

Fundamental Frequency of a String

• A string vibrating with an antinode at its center and a node at each end is vibrating at its fundamental frequency.

Electric Field line

A line drawn in an electric field showing the direction of the force on a positive charge placed in the field

Potential at a point

potential difference between a poimt amd the earth