GCE A LEVEL PHYSICS ALTERNATIVE INTERNAL ASSESSMENT FOR INTENRATIONAL CENTERS [UNIT 6PH07]
ALL Questions and solutions/answers provided. Please reply if you disagree with any solution or have anything to add to i.
Note: Don't bother reading if you haven't sat for the exam yet, because the questions here are not written clearly. Only those who have attempted the paper already will understand the questions and the solutions.
The questions are not VERBATIM as what appeared on the question paper, but the main sense has been implied.
1. Circuit drawn
a) What is the appropriate level for multimeter?
ans: b. 20m
b) Which point is voltmeter set-up on?
ans: b.B [parallel to 110 ohm resistor]
2. Experiment for measuring how intensity of an LED component varies with distance...
a) which is the independent variable?
ans. a. distance
b) which is the dependent variable?
ans. d. resistance of LED
3. Which of the following is not required to measure young modulus?
ans. a. Density
4. A student has to investigate the rate of cooling of a liquid. There are two options: one is to use a data logging device and the other is a student using a liquid-in-glass thermometer and stopwatch.
What are the advantages and disadvantages of these two methods? [4 marks]
[Ans: Advantage of data logging device over other method-- It reduces human error, due to factors such as reaction time. It also records readings very accurately and if connected to a computer, it can easily generate a temperature against time graph.
Disadvantage of data logging device over other method-- It is much more expensive to use than just a thermometer and stopwatch. Moreover, before cooling, the object must have been being heated and after heating finishes, it takes some time for the object to gain all the heat. So, a human will take the time taken for the liquid to stop heating into account but the data logger will not do this.]
5. An apparatus similar to a metre rule is made to measure reaction time. The design is outlined.
a) Using any pair of values, and an equation of motion, show that the values are consistent with each other.
[Ans: use any pair of values for distance and time, and use equation s=ut+0.5gt^2]
b) What are some precautions that would improve the accuracy of the result? [3 marks]
[Ans: The partner must not hold the timer with too much grip (larger area on timer) since this will hamper the distance measurement and also the reaction time measurement. The thumb and the finger of the person testing his reaction time should not have a very large distance, they should be only a slight distance apart before the timer is released to minimise errors.]
c) For a certain person, four values of reaction time are given: 0.18s, 0.19s, 0.20s, 0.08s.
What is the mean time? State the mean reaction time with uncertainty.
[Ans: 0.08s is an anomaly and thus ignored. Mean reaction time is 0.19s. Uncertainty is 0.1s/0.19s=0.5s. Therefore reaction time is: 0.19 plus/minus 0.5 seconds.]
6. About investigating resistivity.
a) Diameter of wire is 0.12 mm, find area.
[Ans: Diameter= 0.00012m, therefore A=pi * (0.00012/2 m)^2= 1.13 * 10^-8 m^2]
b) The length is measured to the nearest 100 mm. Is this an appropriate level of precision or not?
[Ans: Since diameter is in millimetres, and length should also be measured to nearest millimetre not 100 mm (which is nearest centimetre).]
c) Given, gradient of Resistance against Length graph is 4.19 ohm/m , find the resistivity.
[Ans: Gradient of Resistance against length graph is resistivity/area. Since, area is calculated, therefore: Resistivity=Area * Gradient = 1.13093 * 10^-8 * 4.19 = 4.74 * 10^-7 ohm metre]
7. About refractive index.
a) Draw on the given glass block the rays entering, through, and escaping the glass block, and label i and r on the incident ray.
[Ans: Ray entering glass block at angle i to normal, bending towards normal at angle r to normal, leaving glass block and bending away from normal.]
b) Four sets of values of i and r are given. Criticise set of values.
[Ans: There are only 4 sets, there should be more. The values are to the nearest degree, they should be measured to the nearest 0.01 degree for greater accuracy. There is significant gap between each value, there should be more values between the values recorded.]
c) FIll in the table sin i and sin r, and draw the curve of sin i against sin r.
[Ans: Straight line passing through origin with ONE anomalous point.]
d) Should the curve pass through the origin? Justify why.
[Ans: It should pass through origin. According to Snell's Law, sin i is proportional to sin r. OR. It should pass through origin. sin i = refractive index * sin r. This is in the form y=mx+c, where c=0, therefore x-axis intercept at y=0 is 0, thus it passes through origin.]
e) From the graph, find the refractive index of the glass block.
[Ans: Refractive index is found by taking two points (x1,y1) and (x2,y2) on the graph. refractive index = (y2-y1)/(x2-x1). Answer for refractive index is 1.42]
