6 MARKERS Flashcards
discuss which one of the four materials shown on the graph is most suitable for each of the following applications:
- the cable supporting a lift in a tall building
- a rope for bungee jump
[description of graph:
material A, high young modulus but does not undergo plastic deformation
Material B, high young modulus undergoes plastic deformation for a certain extent
Material C, high young modulus undergoes plastic deformation more
Material D, low young modulus (it extends more on y-axis tensile strain than stress ]
Material B/C is used for the lift because has a high young modulus
Material A not chose because low breaking stress
Material A not used because fails without warning
material C not chosen because has a lower breaking stress
material D chosen as due large strain for given stress time taken to come to rest lengthens
not A ,B or C because high Young Modulus so sudden stop resulting in large forces
not A as brittle and therefore limited strain and sudden failure
Discuss the properties of a step-index optical fibre.
Your answer should include:
-the names of the components
-a description of their functions
-a discussion of the problems caused by material dispersion and modal dispersion and how these problems can be overcome.
[6 marks- assessed on quality of written work]
The central part of an optical fibre is referred to as the core and it has the purpose of propagating the light via total internal reflection. Cladding provides a clean boundary for TIR as it has a lower refractive index than the core. It also protects the core from any damage that could lead to signal loss and prevents cross talk between optical fibres.
Material and Modal dispersion both cause pulse broadening which could tamper the signal.
Material dispersion is caused by different wavelengths travelling at differing speeds due to different refractive indices, to prevent use monochromatic light.
Modal dispersion is caused by light entering angles and hence taking different paths. This causes the light to travel in different speeds depending on the angle it has entered the fibre with. To prevent use narrower fibres or single mode fibre as it only allows the light to take one path.
Some subatomic particles are classified as hadrons. There are two classes hadrons.
Discuss the nature of hadrons. Your answer should include: -the identifying properties of hadrons -the structure of a hadron -a discussion of the stability of free hadrons
[6 marks]
Hadrons are particles consisting of quarks that may interact with each other via the strong nuclear force.
Hadrons are classified into baryons and mesons. Baryons are composed by three quarks while mesons are composed by an antiquark and a quark. They are generally unstable with the only exception being protons. Neutrons decay into protons releasing a positron and a neutrino, similarly kaon decays into pions.
Explain, in terms of electron motion, why I-V characteristic for the filament lamp is a curve.
[4 marks- NOT QWC]
An increase in current leads to an increase in temperature which causes ions in the filament to vibrate increasingly, hence, resulting into a higher rate of collisions with electrons. Resistance is therefore increases as shown since V is not proportional to I in this scenario.
Discuss how the discharge tube is made to emit electromagnetic radiation of specific frequencies.
In your answer you should:
- explain why there must be a high potential difference across the tube
- discuss how the energy level diagram predicts the spectrum
- show how one if the wavelengths of light is related to two of the energy levels in the energy level diagram.
[6 marker- based on diagram tbf]
Potential different accelerated electrons so electrons have sufficient energy to excite atoms.
Visible spectrum results from excited electrons moving into the lower level at -3.4eV each transition results into a photon of light, frequency of light in the spectrum, is given by deltaE=hf.
C- energy different in J
lambda= hc/E =660nm
Describe a suitable experiment to determine if a component is an ohmic conductor. Your account should include details of:
- what measurements you would take
- how you would use your measurements
- how you would reach a conclusion
[6 marks QWC]
Set up a circuit with a variable resistor (rectangle with arrow) and a voltmeter in parallel to the component and ammeter in series. Vary current by changing resistance on variable resistor, take repeat readings of pd and current for each resistance and turn off between readings as a rise in temperature would cause resistance to increase. After repeating for a range of resistances, calculate a mean for the pd and current for each resistance. Hence plot pd against current. The gradient corresponds to the resistance and it should go through 0,0 and showcase positive correlation if it is indeed an ohmic conductor.
Discuss the formation of stationary waves on a string or rope. Your account should include:
• a labelled diagram of a stationary wave
• the conditions necessary for stationary waves to form
• a definition of the terms node and antinode
• an explanation of how nodes and antinodes form
[6 marks QWC]
Stationary waves occur when two coherent waves travelling in opposite directions superpose. The nodes are points of minimum disturbance, at this point the two waves experience destructive interference cancelling each other.
Contrastingly, antinodes are points of maximum displacement as the two displacements are in phase hence constructive interference occurs.
An alternating current supply provides an output voltage of 12 V rms at a frequency of 50 Hz. Describe how you would use an oscilloscope to check the accuracy of the rms output voltage and the frequency of the supply.
[6 MARKS QWC]
Connect power supply to the oscilloscope, switch off the time base and adjust y gain in order to get as long a line as possible. The length of the line is to be recorded in order to use it to find peak to peak voltage. Once rms voltage is found, switch on time base and adjust in order to get several cycles on the screen. Use time base setting to find period. Since f= 1/T find hence frequency. Compare with stated value to check accuracy.
Light has a dual wave-particle nature. State and outline a piece of evidence for the wave nature of light and a piece of evidence for its particle nature. For each piece of evidence, outline a characteristic feature that has been observed or measured and give a short explanation of its relevance to your answer. Details of experiments are not required.
[6 MARKS QWC]
Light showcases waves properties through interference. This can be observed through Young’s slit experiment, light forms on the screens luminous fringes defined as maxima divided by dark fringes caused respectively by constructive and destructive interference. If it was a particle only two bright fringes would be able to be observed.
However, it also showcases particle-like nature as it interacts in a 1-to-1 manner with electrons. In order for light to be able to ionise electrons, there’s threshold frequency and intensity doesn’t affect if it will be able or not to ionise electrons. This is observed and defined as the photoelectric effect which proves the expectation of a delayed emission for a low intensity wrong.
Describe the procedure the student would follow in order to obtain accurate and reliable measurements of the resistance of the thermistor at different temperatures.
[6 marks QWC]
Connect the thermistor in parallel to a voltmeter and in series to an ammeter. Place the terminator in a water bath with controlled temperature by using a thermometer to measure temperature. Note down current and pd every time the temperature increases by 5 degrees
On her next jump the gymnast decides to reach a height above position B when jumping on the trampoline. Describe and explain, in terms of energy and work, the transformations that occur as she ascends from her lowest position A until she reaches her new position above B.
[6 marks QWC]
Electrons with a range of kinetic energies strike atoms of a particular element which are in their ground state. As a result of these collisions photons of various frequencies are emitted by some of the atoms.
Explain what is meant by the ground state of an atom and describe the process that is taking place in the atoms emitting photons.
[6 marks QWC]
Describe the procedure the student would follow in order to obtain an I-V curve for the semiconductor diode.
[6 marks QWC]
When monochromatic light is incident on a metal plate, electrons are emitted only when the frequency of light exceeds a certain frequency.
Explain in terms of energy, why this threshold frequency exists and why a photon theory of light provides a better explanation of the photoelectric effect than a wave theory of light.
[6 marks QWC]
Young’s fringes are produced on the screen from the monochromatic source by the arrangement shown in Figure 1 (single slit then double slit).
Explain how this arrangement produces interference fringes on the screen. In your answer, explain why slit S should be narrow and why slits S1 and S2 act as coherent sources.
[6 marks QWC]
