This is revision note that based on CIE A Level Past Paper
Physics Paper 4 O/N 2008
- The formula of the Gravitational Force between the planet and the object :
F = GMm / R^2
- The formula of the centripetal force required for circular motion of the small mass :
F = mRω^2
- The formula of the normal reaction force = GMm / R^2 – mRω^2
- The normal reaction on the mass will have different values at the equator and at the poles because normal to the object become smaller so it 0 at the poles.
- Factors that could, in the case of a real planet, cause variations in the acceleration of free fall at its surface.
>> ‘radius’ of planet varies
>> density of planet not constant
>> planet spinning
>> nearby planets / stars
- The pressure of an ideal gas is decreased at constant temperature. The change in the internal energy of the gas are :
>> kinetic energy constant because temperature constant
>> potential energy constant because no intermolecular forces
>> so no change in internal energy
- The iron-cored transformer is a continuous loop in order to prevent loss of magnetic flux and improves flux linkage with secondary
- The iron-cored transformed is laminated in order to reduces eddy current (losses) and reduces losses of energy (in core)
- The use of Faraday's law to explain the operation of the transformer :
>> changing current in primary gives rise to changing flux in core
>> flux links with the secondary coil changing flux in secondary coil, inducing e.m.f.
- The advantages of the use of alternating voltages for the transmission and use of electrical energy :
>> can change voltage easily / efficiently
>> high voltage transmission reduces power losses
- Evidence of the photoelectric effect for a particular nature of electromagnetic radiation :
>> The rate of photoelectron emission is proportional to the light intensity, I
>> The maximum kinetic energy of photoelectrons depends only on the frequency, and not the intensity of the incident light.
>> The emission of photoelectrons start with no observable time lag at f > fo, even for very low intensity incident light.
>> ‘instantaneous’ emission of electrons
- Lines in the emission spectrum of gases at low pressure provide evidence for discrete electron energy levels in atoms by :
>> Discrete wavelength means photons have particular energies
>> Energy of photon determined by energy change of orbital electron so discrete energy levels
- Electric field --> charged and the force is opposite to the direction of the field.
- Gravitational field --> uncharged and the force is in the direction of the field
- Magnetic field --> charged and there is a force only when the mass is moving
- Magnetic field --> charged and there is no force on the mass when it is stationary or moving in a particular direction.
- Different frequencies and wavelength are used in different channels of communication.
- Infra-red radiation rather than visible light is usually used with optic fibres because infrared has less attenuation so fewer repeater amplifiers needed or longer uninterrupted length.
- The base stations in the mobile phone networks operate on UHF because it have limited range so cells do not overlap or it have short wavelength so convenient length aerial on mobile phone.
- For satellite communication, frequencies of the order of GHz are used, with the uplink having different frequency to the downlink because it have large bandwidth / large information carrying capacity different so that uplinks signal not swamped by downlink.
- The point 'something' is referred to as virtual earth because :
>> the gain of op-amp is very large
>> non-inverting input is at Earth 10 V
>> for amplifier not to saturate, Point must be about earth / 0 V
- The variation of the voltmeter reading as the lamp is moved away from the LDR :
As the lamp is moved away from the LDR, its intensity will decrease, so the resistance of the LDR will increase. Therefore its output voltmeter reading will increase.
- The difference between the image produced by the CT scanning and X-ray imaging :
CT scanning use several slices produces three dimensional image, while X-ray produces two dimensional image. The image in CT scan is more precise than X-rays.
- CT scanning could not be developed before powerful computers were available because :
>> X-ray image of slice taken from many different angles
>> these images are combined (and processed)
>> repeated for many different slices
>> to build up a 3-D image
>> 3-D image can be rotated
>> computer required to store and process huge quantity of data
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