rip 2.0 Flashcards
Explain why this circuit will provide data for large V values but not for small V values
With the variable resistor set at zero, the p.d. across the resistor is zero, so p.d. across lamp is 2.4V / large.
With the variable resistor set at its maximum value, there is a p.d. across the variable resistor, so p.d. across the lamp is not small.
explain how the wavelength of the light changes as light travels from glass to water.
The ray is refracted away from the normal, therefore the refractive index of water is less than the refractive index of glass or speed of light in water is greater than the speed of light in glass.
The frequency remains constant.
v = fλ and therefore the wavelength of light increases as it travels from glass to water.
Explain how you can use an oscilloscope set to a time-base of 0.1 ms div-1 to check that the frequency of sound is 2.8 kHz.
Place a microphone close to loudspeaker and connect it to the oscilloscope.
Measure the number of divisions between neighbouring peaks of the signal. (AW)
The separation between the neighbouring peaks should be 3.6 divisions
Explain how the arrangement shown in Fig. 18 produces an interference pattern along the line XY.
The sound is diffracted at each slit.
The diffracted waves interfere in the space beyond the slits.
There is loud sound / maxima / constructive interference when phase difference is zero or when path difference nλ.
There is quiet sound / minima / destructive interference when phase difference is 180°
State what is meant by the decay constant of an isotope.
The decay constant is the probability of decay of a nucleus per unit time.
Explain how the graph in Fig. 20 can be used to determine the half-life of protactinium.
- A = A0e-λt
- lnA = lnA0 - λt
- A graph of lnA against t will be a straight line
with gradient (-) λ - half-life = ln2/λ
Describe the motion of the particle in terms of the force it experiences when the field is
(i) a magnetic field
(ii) an electric field.
i- The force is right angles to the motion / velocity.
The particle describes a circle in the plane of the paper.
ii- Particle experiences a force perpendicular to motion/velocity.
It moves to the right and either comes out or goes into the plane of the paper (in a parabolic path).
State what is meant by induced nuclear fission.
The splitting of a (uranium) nucleus as a neutron is absorbed (into two fragment nuclei and neutrons).
Explain the role of the moderator and the control rods in a nuclear reactor.
The moderator slows down the fast-moving neutrons.
The neutrons lose significant amount of their kinetic energy when colliding with moderator nuclei.
or
The moderator does not absorb the neutrons
The control rods absorb the neutrons.
The rate of fission reactions is less / reduced.
Discuss how the actual value of the resistivity of the metal would differ from the value calculated
The actual resistance values will be smaller.
The gradient of the graph will be lower.
Hence resistivity of the metal will be smaller than the value calculated
Explain the observations above and refine the circuit design so that the brightness of the lamp can be varied as the slider is moved from A to B.
The voltmeter has large or infinite resistance.
Hence the p.d across the lamp or current in the lamp is small or zero (and the lamp is not lit).
Refining design: remove voltmeter from the circuit or place the voltmeter across the lamp.
The voltmeter has very high resistance and has a full scale deflection (f.s.d.) of 6.0 V.
Explain how the circuit works and use calculations to discuss a significant limitation of this design.
- Total resistance decreases as temperature
increases (allow reverse argument) - Current in circuit increases as temperature
increases or p.d. is in the ratio of the resistance values - Therefore, the p.d. across resistor increases
or p.d. across thermistor decreases. - The change in resistance is small when
resistance of thermistor changes from 200 °C to 300°C - Change in voltmeter reading is too small over
this range - Non-linear change of resistance with
temperature.
Explain how the stationary wave is formed on this stretched string
Waves are reflected at the pulley end.
This produces nodes and antinodes on the string.
Describe and explain how the capacitor plates A and B acquire opposite charges
Electrons in the circuit move in a clockwise direction and electrons are deposited on plate B.
(An equal number of) electrons are removed from plate A giving it a positive charge (of equal magnitude).
Describe how the time constant of this circuit can be determined experimentally in the laboratory.
Connect a voltmeter or data-logger or oscilloscope across the resistor (or capacitor) or an ammeter in series with the resistor.
A stopwatch is started when the switch is opened and stopped when the p.d. or the current to decreases to 37% of its initial value.
The time constant is the time taken for the p.d. or the current to decreases to 37% of its initial value
Describe the similarities and the differences between the gravitational field of a point mass and the electric field of a point charge.
Similarity
The field strength or force is dir prop to 1/separation2 or both produce a radial field.
Differences
Gravitational field is linked to mass and electric field is linked to charge.
Gravitational field is always attractive whereas electric field can be either attractive or repulsive
Explain why the spheres are separated as shown
The charges repel each other (because they have like charges).
Each charge is in equilibrium under the action of the three forces: downward weight, a horizontal electrical force and an upwardly inclined force due to the tension in the string
Describe an experiment that can be carried out to determine the half-thickness of lead and how you would use your results with Fig. 23.1 to determine the energy of a gamma photon from a radioactive gamma source in your laboratory
- GM tube, counter or rate-meter and lead
plates used - Micrometer or vernier calliper (to measure
thickness of plates). - Measure counts for a specific time and hence
the count-rate for each thickness of lead - Vary the thickness of lead and record the
count-rates - Plot a graph of count-rate against thickness
and determine the half thickness of lead
. - Do not point source at person
- Keep safe distance between you and source
- Use tongs to handle source.
- The counts are recorded over a long period of
time - Background radiation taken into account.
State the principle of superposition of waves.
(When two or more waves meet at a point in space) the
resultant (displacement) is equal to the (vector) sum of the individual displacements of waves (meeting at a point)
The blue light is now replaced by a similar beam of red light.
State and explain the effect, if any, on the fringes observed on the screen.
Red light has longer wavelength and separation
between fringes increases
Separation between fringes justified in terms of x is dir prop to wavelength.
D and a are constants
The instrument used to measure d has a zero-error. The measured d is much larger than the actual value. Discuss how the actual value of R compares with the value calculated above.
(The actual) R is large(r) because (the actual) d is
small(er)
The e.m.f. of the variable supply is now slowly decreased from 4.2 V to 0 V.
Describe the effect on the current I in the 33 Ω resistor.
Any two from: The current decreases up to 1.5 V The current is zero at 1.5 V The current changes direction / is negative when < 1.5V The current increases below 1.5 V
The group of students know that maximum power is dissipated in the variable resistor when R is equal to the internal resistance r of the cell.
Describe, with the help of a suitable circuit diagram, how the students may have determined P and R. Use Fig. 18.2 to estimate the internal resistance r of the cell and discuss any limitations of the data plotted by the group
Correct circuit with (variable) resistor, ammeter and
voltmeter
R changed to get different values for P
R = V/I (using ammeter and voltmeter readings) or R
measured directly using an ohmmeter with the variable resistor isolated from the circuit or R read directly from a resistance box
Power calculated using P = V2
/R or P = VI or P =I2R
The value of r is between 1.0 to 3.0 ohm
A smooth curve drawn on Fig. 18.2 (to determine r)
A better approximation from sketched graph or r is
between 1.5 and 2.7 ohm
Any attempt at using E = V +Ir, with or without the
power equation(s) to determine r - even if the value is incorrect
Limitations:
‘More data’ required
Data point necessary at R = 2.0 ohm/ More data
(points) needed between 1 to 3 ohm
No evidence of averaging / Error bars necessary (for
both P and R values)
Define electric potential at a point in space.
(Electric potential) is the work done per (unit) charge in
bringing a positive charge from infinity (to the point).
