# Physics OCR Unit 1 (PIA G491)

everything in this unit

?
• Created by: emilyanne
• Created on: 13-05-12 18:09

## IMAGING AND SIGNALLING 1

converging lenses:

light radiates as wavefronts which are curved. curvature decreases as they travel away from source. LENSES are to INCREASE or DECREASE curvature.

CONVERGING LENSES add curvature and focus them to a point (distance between point and lends is FOCAL LENGTH) and form a real image.

digital storage:

a PIXEL is what makes up a digital image and has an assigned value (the number of BITS which is 0 or 1.)

the number of values=2^(number of bits)

rates of information of transfer: bits per second.

quality of digital image increased by taking average of pixels around each pixel (including the one itself) and averaging them.

1 of 6

## IMAGING AND SIGNALLING 2

digitsing:

digitising a signal from analogue: samples are taken at regular intervals and stored as a number of bits. (if not enough samples then it will not be reproduced very clearly)

sampling rate: samples per second (same as frequency) in Hz.

spectrum: the presence of a range of frequencies.

fundamental frequency: lowest frequency which makes up the signal.

polarisation of waves:

TRANSVERSE WAVES (perpendicular to direction of energy) can be polarised (which means waves vibrate in the same direction)

2 of 6

## IMAGING AND SIGNALLING 3

terminology and equations:

byte is 8 bits.

magnification is (image height)/(object height).

resolution is smallest physical change a sensor can detect.

sensitivity is the amount of electrical change per physical change outputted.

refractive index is (speed of light in material)/(speed of light in vacuum).

amount of info in image: no of pixels x bits per second.

v(elocity) = f(requency) x λ (wavelength).

min rate of sampling should be bigger than or equal to 2 x max freq of signal.

rate of transmission of digital information = samples per second x bits per sample.

3 of 6

## SENSING

terminology, concepts and equations:

current, I, is flow of charged particles.

potential difference, V, is energy per unit charge.

resistance is caused by electrons colliding with other electrons and particles.

conductance is how much an electrical component carries an electircal current.

IN SERIES, total R = R1 + R2 + R3 + ...

IN PARALLEL, total G = G1 + G2 + G3 + ...

emf is pd across a cell.

Ohm's law is that V = IR, and for potential dividers V2 = V(total in) x R2/(R1+R2).

load resistance is resistance across a power source.

4 of 6

## DESIGNER MATERIALS 1

terminology:

stiffness is resistance of a material to deformation.

ductile is that it can be shaped without breaking (undergoes deformation before breaking).

hardness is that it cannot easily be scratched.

toughness is when a material is resistant to fracturing. (area under a stress/strain graph and the opposite of brittle).

elastic: returns to original dimensions when force is removed.

plastic: dimensions have changed when force is removed.

stress: measurement of strength. =F(orce)/A(rea cross sectional).

strain: how much a material stretchs. =x (extension)/ L (original length)

5 of 6

## DESIGNER MATERIALS 2

terminology:

young's modulus: measure of stiffness. stress/strain.

the graph has a steep gradient to start (elastic region) and then is flatter (plastic region).

properties:

METALS: ductile, elastic to a point, stiff (because of positive ions and negative electron attractions)

POLYMERS: long chain molecules. insulator (no free electrons), elastic (long chains), stiff (long chains tangle up).

6 of 6

Report