Physics Paper 2 Questions and Answers - Form 3 End Term 2 Exams 2023

Section A (25 marks)

1. Give one difference between luminous and non-luminous sources of light. (1mk)
2.  When a negatively charged rod is brought near the cap of a leaf electroscope, the leaf rises.
   Explain this observation, (2mks)
3. Figure 2 represents a displacement-time graph for a wave.
   
   
   Determine the frequency of the wave. (2mks)
4. State the conditions necessary for a wave incident on a slit to be diffracted. (2mrks)
5. In an experiment to determine the focal length of a concave mirror, magnification M was determined for various image distances v. Figure 3 shows a graph of magnification M against image distance v for the results from the experiment.
   
   
   Given that M = 1 ^v/_f determine the focal length f of the mirror. (3mks)
6. A hair dryer is rated 2500W, 240V. Determine its resistance. (2mks)
7. Figure 4 shows the magnetic field pattern round a current-carrying conductor. Indicate on the conductor the direction of the current. (1mk)
         
   Figure 4
8. Why is repulsion the sure test for a magnet? (1mk)
9. Figure 5 shows a ray of light incident on an air bubble which is inside water,
   
   Complete the ray to show the path it follows through the air bubble. (1mk)
10. Explain how polarization of a cell increases the cell’s internal resistance. (2mks)
11.  
    1. A positively charged material was brought close to an insulated metallic ball as shown in Fig 4. State and explain the distribution of charge in the ball (2mks)
       
    2. Explain why sound cannot be heard from far when one shouts in a forest (1mk)
12. Using the variation of resistance with temperature, differentiate between a conductor and a semiconductor. (1mk)
13. A cell of internal resistance O.5 ? is in a circuit containing a 10 ? resistor. A current of 2A flows in the circuit. Determine the emf of the cell. ( 2mks)

Section B (55 marks)

14.  
    1.  
       1. State Snell’s law of refraction of light (1mk)
       2. Give two advantages of totally internally reflecting prisms over plane mirrors. (2mks)
    2. A ray of light is incident on a kerosene water interfaces as shown in 
       
       Given that the refractive index of water and kerosene are 1.33 and 1.44 respectively,
       Determine
       1. the refractive index for the kerosene – water interface (3mks)
       2. determine and show on the figure the path of the rays of light between the Kerosene-water surface (3mks)
       3. Why does the colours of the light separate at the kerosene layer. (1mk)
       4. State and explain the observation that the eye above the two surfaces would see (2mks)
15.  
    1. State Ohm’s law (1mk)
    2. The figure 8 below shows a circuit with a coil used to warm oil in a beaker.
       
       1. Explain how heat is produced in the coil (2mks)
       2. Given that the reading of the ammeter is 2.4A determine the resistance of the coil. (3mks)
       3. How much heat is produced in the coil in a minute? (3mks)
       4. Give two changes that can be made in the set up in order to produce more heat per minute. (2mks)
16.  
    1. Define capacitance of a capacitor (1mk)
       The figure below shows a charged electroscope two aluminium plates A and B arranged a shown
                 
       State and explain the observations made when:
       1. d is reduced (2mks)
       2. the plate A is more horizontally (2mks)
       3. a sheet of polythene is placed between A and B (2mks)
    2. Three capacitors are connected to a 10V battery as shown below.
                 
       1. Calculate the combined capacitance (3mks)
       2. What is the charge on the 3 μF ? capacitor (3mks)
17. Students set up a mass attached to spring such that when it oscillates it taps on water surface in a wide shallow tank.
    
    The students measured time for 20 oscillations and found that the mass takes 36 seconds.
    1. Determine the periodic time of the mass (2mks)
    2. Calculate the frequency of the waves produced on the water surface (3mks)
    3. Given that the student counted four ripples between the mass and end B of the tank,
       Determine the speed of the waves. (3mks)
18.  
    1. A machine is a device that enables work to be done more easily and conveniently. State any two ways in which a machine makes work easier. (2marks)
    2. Figure 7 shows a wheel and axle being used to raise a load W by applying an effort E. The radius of the wheel is R and of the axle is r.
                      
       1. Show that the velocity ratio (V.R) of this machine is given by ^R/_r  (3 Marks)
       2. Given that r = 5cm and R = 50cm, determine the effort required to raise a load of 200N if the efficiency of the machine is 90%. (3 mks)
    3. An airtight flask containing a gas is connected to a mercury manometer. The levels of mercury in the two limbs of the manometer are as shown in the diagram below.
                       
       Calculate the pressure of the gas (Density of mercury = 1.36 x 10 4 kg/m 3 and atmospheric pressure = 1.0 x10 5 N/m 2 ) (3mks)
    4. State one way of making the surface tension of a liquid stronger               (1mk)

MARKING SCHEME

SECTION A

1	A lumious source of light emits light while a non-lumious source reflects light	1mks
2	Electrons are repelled from the cap and flow to the leaf and plate. Repulsion between  the electrons on the plate and those on the leaf causes the leaf to rise.	2mks
3	f =  Number of waves         =    1¾       = 50H3                   Timetaken                   35 x 10–3  Alt.       f = 1  =      1                             T        (25 – 5) x 10–3 = 50H3	2mks
4	Width of the aperture/ slit should be approximately or nearly equal to λ of the incident wave;	2mks
5	0.9 – 0.4         – 1 Slope =     3 –  7       =     f           =   – 0.5                   5     =  0.125          f = 8cm	3mks
6	v2                  v2 = 2402      p =    R           R =  P     2500                               = 24.04Ω	2mks
7		1mk
8	Repulsion only occurs between like poles of magnets while attract also occur between a magnet and a magnetic material	1mk
9		1mk
10	Hydrogen gas bubbles form around the positive plate. The hydrogen gas insulates the positive plate thus increasing internal  resistance	2mks
11	Electrons are attracted towards the rod leaving the atoms at the other end of the ball with net positive charges  Trees absorb sound	2mks 1mks
12	In conductor the resistance increases with increase in temperature while in a semiconductor the resistance reduces with  increase in temperature.	1mk
13	E = Ir + IR      = 2 x 0.5 + 2 x 10     = 11V	2mks
	SECTION B
14	The ratio of the sine of angle of incidence to the sine of angle of refraction is a constant for a pair of media Do not absorb light energy like mirrors Not affected by thickness as mirrors Do not wear off like the peeling of siyvering on mirror.   k°w = k°a a°w = 1    x 1.33 = 0.9236  1.44 = 70° Sini = 0.9236 Sinr Sin r   = sin 70° = 1.0174 0.9236 r is greater than 90° hence the light reflection The different colours travel at different velocities hence would have different angles of refraction and are dispersed The eye would see a spectrum since the light rays are dispersed in the kerosene layer and are internally reflected at the kerosene – water surface the eye would see a spectrum at the surface	1mk 2mks 3mks 1mk 2mks
15	Current flowing through a conductor is directly proportional to the potential difference across it provided the temperature and other physical conditions are kept constant   The work done in driving charges through the coil is high due to its resistance. This energy is converted into heat in the coil V = IR            R = V      = 12V                              I           2.4                                      = 5.0Ω H = VIt H = 12 x 2.4 x 60 = 1728J Using a source with higher emf Reducing the length of the coil = P = V2           R	1mk 2mks 3mks 3mks 2mks
16	capacitance c is the charge stored in a capacitor per unit voltage the deflection of the leaf decreases since the pd reduces with the distance of separation, the greater the deflection, the smaller the capacitance. the deflection of the decreases since the pd increases with the area of overlaps or the greater the deflection the smaller the capacitance. the deflection of the leaf decreases, the capacitance increases ,since the smaller the deflection the greater the capacitance.                 C2C3     C = C1 + C2 + C3          μF + 4 x 4       =3       4 + 4       =3 μF + 2μF       =5 μf Charge on the 3 μF capacitor is the same as the overall charge Q =CV                                                                                                           =5.0 x 10                                                                                                           =50C	1mk   2mks 2mks   2mks 3mks       3mks
17	T = T = 36 = 1.8s       20   20 f = 1 = 1 = 0.5556Hz       T   1.8 80cm ⇒ S4λ V = fλ = 1 x 0.2 = 0.111m/s   1.8	2mks 3mks   3mks
18	A small force (effort) is used to overcome a large force (Load) Less energy is expended in doing work Less time is used in accomplishing the task In one revolution, both wheel and axle complete one circumference  V.R = Effort Distance/Load distance = 2 πR/2πr V.R = R/r V.R = 50/5 = 10 M.A = efficiency x V.R/100 = 90x10/100 = 9 Effort = Load/M.A          = 200/9             = 22.22N Gas Pressure = At.Pressure – Pressure due to Hg Volumn Pg = 1.0x105 – 0.4 x 13600x10 = 94560N/m2 By lowering the temperature of the liquid	2mks     3mks   3mks   3mks   1mk