Physics Revision

Topic 1: Physics and Physical Measurement:

The realm of physics:

The order of magnitude is i.e. 10x.

Range of masses (kg): 10-32 (electron) to 1052 (mass of the observable universe)

Range of lengths (m): 10-15 (diameter of proton) to 1026 (radius of universe)

Range of times (s): 10-23 (passage of light across a nucleus to 1019 (age of the universe)

Measurement and uncertainties:

Fundamental units:

Derived units are different combination of the fundamental units

For example speed = distance/time = meters/seconds =m/s =ms-1

Remember to state answers in the format ms-1

Important Prefixes:

Random errors are errors in measurement caused by different factors

Random errors include the readability of the instrument and the effects of a change in surroundings. Repeated readings do reduce random errors.

Systematic errors are errors due to faulty equipment/calibration.

Systematic errors include an instrument being wrongly calibrated. Repeated readings do not reduce systematic errors.

Individual measurements: the error is ± the smallest value e.g. .5mm

When we take repeated measurements and find an average, we can find the uncertainty by finding the difference between the average and the measurement that is furthest from the average.

A precise experiment is one with a small random error, i.e. the more significant figures the more precise.

An accurate experiment is one with a small systematic error, i.e. the nearer the real value the more accurate.

Give answers to the same amount of significant figures as the least precise value used.

If you have the measurement for a football pitch of 100m±1m

The absolute uncertainty is 1m

The fractional uncertainty is 1/100 = .01

The percentage uncertainty is .01 x 100 = 1%

For addition and subtraction, the absolute uncertainties can be added

Magnitude force on a current: Magnitude of the electric field: (B) = F/ILsin(O)

I=Current

L=Length of Current

Sin (O) = sin of the angle between the field and current

F=BIL sin (O) where F is in (T) for tesla.

Magnetic Force on a Moving Charge:

F=Bqv

B=magnitude of magnetic field

Q= magnitude of charge

V=velocity of charge

=Circular motion

Topic 7: Atomic and Nuclear Physics:

The atom

Rutherford Model of the atom: the atom consists of a small dense positive nucleus, surrounded by electrons that orbit the nucleus (as planets orbit the sun) as result of electrostatic attraction between the electrons and the nucleus.

Evidence supporting the nuclear model of the atom:

Geiger-Marsden Experiment:

Alpha particles were fired at a golf-leaf. Due to the size and velocity of the particles most were expected to travel straight through. However some alpha particles were deflected through huge angles caused partly by a dense, positive nucleus

One limitation of the simple model of the nuclear atom:

Did not explain why electrons surrounding the nucleus were not drawn into the nucleus by strong electrostatic attractions to the protons of the nucleus.

Did not specify composition of nucleus.

How did protons in the nucleus stay closely bound when electrostatic forces should have forced them apart?

Emission Spectra: the spectrum of light emitted by an element

Absorption Spectra: a bright continuous spectrum covering the full range of visible colors, with dark lines where the element absorbs light

Evidence for the existence of atomic energy levels:

The emission spectra of each element is unique as electrons can only occupy specific energy levels.

Movement between energy levels requires electron to emit or absorb energy. Energy emitted or absorbed is in the form of packets of light called photons. E=hf (Energy of a photon = Planck’s constant*frequency of light in Hz).

If laser light is shone through a grating on to a screen, you will see just how sharp and spaced out are the maxima

Measuring the line spacing and the distance of the screen from the laser, the wavelength of the laser can be measured.

OR:

If white light is incident on a diffraction gradient the angle at which constructive interference takes place depends on wavelength

Different wavelengths are observed at different angles

An accurate measurement of the angle provides an accurate measurement of the exact wavelength and colour of light considered.

Spectrometer used to achieve an accurate measurement

G5

G.6.1: Explain the production of interference fringes by a thin air wedge

When the monochromatic light strikes the glass plate some of it will be reflected down onto the wedge.

Some of the light reflected from the wedge will be transmitted through the glass plate to the travelling microscope.

A system of equally spaced parallel fringes (fringes of equal thickness) is observed.

The travelling microscope enables the fringe spacing to be measured. The fringes can also be observed by the naked eye

Explain how wedge fringes can be used to measure very small separations.

Applications include measurement of the thickness of the tear film on the eye and oil slicks.

Describe how thin-film interference is used to test optical flats

Wedge films can be used to test optical surfaces for flatness.

If a wedge is made of two surfaces one of which is perfectly plane but the other has irregularities, the observed fringe pattern will be irregular in shape. The irregular surface can then be re‐polished until the fringes are all completely parallel and of equal thickness

State the condition for light to undergo either a phase change of π, or no phase change, on reflection from an interface

When light is reflected back from an optically denser medium there is a phase change of π

When light is reflected back from a optically less dense medium there is no phase change

Option H: Relativity