Physics Paper 3 Mistakes- Turning Points Flashcards
Describe how Newton’s theory of light was used to explain the refraction of light as it moves from air into glass
Light is made of corpuscles
When corpuscles meet the boundary:
Component of velocity parallel to surface unchanged
Component of velocity perpendicular to surface increases
There is a force of attraction to the surface.
Light bends towards the normal and light travels faster in glass
Describe a demonstration using visible light that can be performed in a school lab to show Newton’s theory of light is not correct
Describe diffraction experiment.
There is a series of maxima and minima formed and a bright spot in centre of double slit formed.
Diffraction is a wave phenomenon.
If light was made up of particles, there would be 2 bright spots and no bright spot in the centre.
One postulate states that the physical laws have the same form in all inertial frames. State the other postulate and explain how it is consistent with Maxwell’s formula for the speed of light.
Equation only contains constants and constants do not depend on reference frame
OR
Speed of light is invariant in all reference frames. Speed of light in free space is constant.
The student observes 2 bright white lines on the screen. Explain how this observation supports Newton’s theory of light.
His theory said light was made of corpuscles that travel in straight lines.
This meant there would be no diffraction and only 2 bright white lines would be seen
Outline the key features of Huygens wave theory and how the double slit experiments’ results support the theory.
Explanation of theory:
Light is a wave
Theory uses idea of secondary wavelets.
Each point. on a wavefront acts as a source of secondary wavelets.
How it supports Huygens’ theory:
Each point at the slit produces secondary wavelets.
Wavelets overlap on scree.
There is a path difference and therefore a phase difference.
Bright fringes where….. dark fringes where…..
Newton’s theory and Huygen’s theory make different predictions about the appearance of light on the screen. Discuss these differences in appearance.
Newton : predicts bright central spot surrounded by partial shadow
Huygen : predicts bright region with fringes around the edge and the edge of the bright fringes are coloured
State and explain the sign of the charge on the oil droplet when it is stationary between two horizontal metal plates, with the top plate being positive.
The oil drop is stationary so the electric force is in the opposite direction to the weight.
Top plate is positively charged and the force is acting up towards the positive plate so Q is negative
State what f0 represents in the equation c = 4dnf0
Frequency of rotation of the toothed wheel when no reflected is seen.
This is the lowest frequency
State how e0 and u0 are related to the types of field in a wave.
e0 relates to the electric field strength in free space.
u0 relates to the magnetic field strength around a current carrying wire in free space
KE of a particle moving at relativistic speeds
KE = m0c^2 / sqrt( 1 - v^2/c^2) - m0c^2
Discuss the change in observed mass of a spring when it is stretched
Mass is related to energy through E = mc^2
When a spring is stretched it gains elastic potential energy and therefore mass increases
Explain how measurements in the circuit and the diffraction pattern produced on the screen by electrons can be used to support the De Broglie hypothesis
De Broglie hypothesis suggests wavelength will decrease if momentum increases.
Measure the voltage (across the anode) to determine the KE of the electrons and therefore their momentum.
Measure ring diameter as increased diameter suggests increased wavelength.
Hypothesis supported by increasing voltage resulting in decreased ring diameter.
What is a relevant property of moving electrons in a STM microscope
Moving electrons can cross a potential barrier
What is a relevant property of moving electrons in a TEM microscope
Moving electrons can be deflected by a magnetic field
T is a radiowave transmitter with an aerial consisting of two vertical metal rods.
D is a detector that uses conducing loop aerial.
T is switched on so that an oscillating current is produced in the metal rods. An EMF is detected in the conducting loop aerial.
Explain this experiment with reference to Maxwell’s model of EM waves
Maxwells model has varying perpendicular E and B fields.
Oscillating current in T indicates presence of oscillating E field.
Oscillating current in T produces a B field.
Varying B field induces varying EMF in loop.
State what is meant by an inertial frame of reference
One which moves at constant velocity.
Describe how a cathode ray is produced in the discharge tube
The electric field ionises the gas atoms.
Electrons are attracted and accelerated to anode.
Positive ions are attracted and accelerated to cathode.
Electrons are released from the cathode and are accelerated to the anode
Discuss the significance of Thomsons results for the particles in cathode rays, when compared with the specific charge of the hydrogen ion.
Specific charge much greater (approx x2000) than the specific charge of a hydrogen ion.
Cathode rays particles mass much smaller than hydrogen ion and therefore smaller than an atom
State what is meant by black-body radiation
EM radiation spectrum with peak depending on the temperature of the emitter alone
Describe how the predictions of classical theory compare with Wien and Lummer’s experimental results
Intensity similar at long wavelengths.
Theory predicts intensity increases at shorter wavelengths and is infinite at very short wavelengths.
Outline the main aspects of Planck’s suggested solution to the problems of classical theory
EM radiation is emitted in quanta.
Energy of quantum is related to a single frequency
E = hf where h is Planck’s constant
The scanning tunnelling microscope (STM) uses a process called quantum tunnelling.
Explain what is meant by quantum tunnelling of an electron in an STM
Electrons in surface have to overcome the potential barrier.
Electrons have insufficient energy so there is a probability of electrons crossing from sample to tip, due to the wave properties of electrons
Describe how the STM creates a map of the positions of one row of atoms on the surface of the sample
Tip of probe maintained a certain distance above surface.
When probe moves over higher layer of electrons, current increases.
Tip is moved higher to reduce current to original value
