BTEC Applied Science - Unit 1 - Physics

periodic time

the time taken (in seconds) for one complete cycle of a wave, vibration, or oscillation

T = 1/f

time period, T (in seconds) and frequency, f (in hertz)

wave speed

the distance in metres (m) travelled by a wave in one second (s)

wavelength

the distance (in metres) between two nearest corresponding points on a wave, e.g. the distance between two peaks (crests)

frequency

the number of waves produced in one second or the number of waves that pass a point each second

amplitude

the maximum displacement of a wave from its undisturbed position

oscillation

a regular repetitive motion, e.g. a weight on a spring bouncing up and down, or a pendulum swinging backwards and forwards

transverse

a wave in which the direction of oscillations is perpendicular (at right angles) to the direction of the wave

longitudinal

a wave in which the direction of oscillations is parallel to the direction of the wave

displacement

the oscillating distance of a point on a wave from its undisturbed position

coherence

two or more sources of waves that have the same frequency and are in phase or have a constant phase difference

path difference

the difference between the distances that two waves have travelled when they meet at a point (usually measured as a multiple of wavelengths)

phase difference

the amount by which one wave leads or lags (falls behind) another wave (usually measured in degrees, where 360⁰ corresponds to one full wave cycle)

in phase

when two waves have zero phase difference

antiphase (completely out of phase)

when two waves have a phase difference of 180⁰ (half a wave cycle)

superposition

when two or more waves combine; their displacements are added together (displacements can cancel each other out)

constructive interference

when the superposition of two waves cause the displacement to increase (greater amplitude)

destructive interference

when the superposition of two waves cause the displacement to decrease (smaller amplitude, even zero)

diffraction grating

an optical device that has a periodic structure of many slits which splits and diffracts light into several beams. Different frequencies (wavelengths) of light diffract by different amounts

(atomic) emission spectra

the range of frequencies of light emitted by an element because of electrons moving between energy levels within atoms

identifying gases

each element has a unique emission spectra and so by analysing the light given off all the elements can be identified

wave equation

v is the wave speed (velocity) in metres per second (m/s), f is frequency in hertz (Hz), and λ is wavelength in metres (m)

stationary (standing) wave

the superposition of a wave and its reflection to form a steady interference pattern of nodes and antinodes

node

points on a stationary wave with zero amplitude (two nodes are half a wavelength apart)

antinode

points on a stationary wave with maximum amplitude (two antinodes are half a wavelength apart)

resonance

when a system is periodically forced at a frequency that causes a massive increase in amplitude (e.g. when you push someone on a swing)

speed of wave on a string

v is the wave speed (velocity) in metres per second (m/s), T is the tension in the string in newtons (N), and 𝜇 is the mass per unit length of the string in kilograms per metre (kg/m)

refraction

the change in direction of light (a wave) when there is a change of speed as it crosses a boundary between different media (e.g. passing from air into glass)

refractive index (of a medium)

the ratio of speed of light in a vacuum, c, to the speed of light in the medium, v. (c/v)

total internal reflection

when light reflects within a medium (of greater refractive index) instead of refracting across the boundary into another medium (of lower refractive index)

critical angle

the angle of incidence that causes an angle of refraction of 90⁰, total internal reflection occurs when the angle of incidence is greater than the critical angle

optical fibre

thin fibre of glass that relies upon total internal reflection so light rays can pass down the length of it

endoscope

an optical device made of bundles of optical fibres. Light is sent into a hard to see place (usually the body) it then reflects and returns via a second bundle of fibres

analogue signal

a signal that continuously varies in both amplitude and frequency

digital signal

a signal that is made up of a stream of binary data in the form of zeros and ones

analogue-to-digital conversion

analogue signals are sampled (values taken) continuously at fixed intervals of time. The values are then converted into binary values (1s and 0s) so they can be sent as a digital signal

electromagnetic spectrum

there are seven types of electromagnetic waves, each with a range of frequencies, that make up a spectrum; radio-waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays

speed of light (in a vacuum)

all electromagnetic waves travel at the same speed of light in a vacuum, 3x10⁸ m/s

inverse square law

k is a constant (does not change) for a particular source of a wave, the intensity of a wave will reduce in line with the square of the distance, r. (E.g. if the distance doubles then the intensity will reduce by a factor of 4)

kilohertz (kHz)

1,000 Hz (kilo = 1,000)

megahertz (MHz)

1,000,000 Hz (mega = 1 million)

gigahertz (GHz)

1,000,000,000 Hz (giga = 1 billion)

terahertz (THz)

1,000,000,000,000 Hz (tera = 1 trillion)

satellite communication

high powered microwave and radio-wave signals are used to communicate long distances with satellites. Upload and download signals are transmitted at different frequencies. Radio-waves can be used for low orbit satellites. Microwaves are needed for high orbit satellites so that the signal can pass through the atmosphere

mobile phones

base stations transmit and receive signals over a limited range and allow phones to communicate across phone provider networks, which are allocated a band of frequencies in the radio/microwave region

Bluetooth

lower power devices communicate over a short range (about 10 m) directly with other devices e.g. mobile phone to ear buds. 'Frequency-hopping' is used to reduce interference with Wi-Fi signals that use similar frequencies of microwaves

Wi-Fi

computers and mobile devices can connect using a medium power signal to the internet via a router over a range of 100 m

infrared

low power devices like remote controls can send signals over a short range, but these signals require 'line-of-sight' and so are easily blocked and do not work well in bright sunlight