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

INSTRUCTIONS TO THE CANDIDATES:

• Answer all the questions both in section A and B in the spaces provided below each question
• All workings must be clearly shown; marks may be awarded for correct steps even if the answers are wrong.
• Mathematical tables and silent electronic calculators may be used.

SECTION A : (25 Marks)

1. The figure 2 below shows two plane mirrors inclined at an angle X from each other. A viewer counts a total of seven images from looking directly from each of the object O. Determine the value of X.  (3 marks)
                                                               
2. Two pins are hanging from a magnet as shown in the diagram below.
                                                                         
   Explain why they do not hang vertically downwards. (2 marks)
3. State two similarities of images formed by a plane mirror and a convex mirror. (2 marks)
4. State the two Laws of refraction (2 marks)
5. Calculate the angle of refraction for a ray of light from air striking an air-glass interface, making an angle of 60° with the interface. (_an_g = 1.5) (2 marks)
6. A student was investigating the brightness of bulbs when set up in different circuits. He used identical bulbs and cells. He set up circuits A and B as shown in figure (A) and (B) below.
                                                                  
                                                                                        A                                                                      B
   State and explain which set up had the bulbs light brightest. (2 marks)
7. A radio signal of 30MHz is received by an aerial whose length is 1/8 ^th of its wavelength. If the speed of light is 3.0 x 10⁸ m/s determine the length of the aerial. (3 marks)
8. A boy stood 3m from a large concave mirror of focal length 5m. State two characteristics of his image. (2 marks)
9. State two characteristics of sound waves. (2 marks)
10. A negatively charged object was brought near a charged electroscope. The leaf was observed to fall then rose.
    1. State the charge of the electroscope …………………………………….. (1 mark)
    2. Compare the magnitude of charge of the object with that of the electroscope.(1 mark)
11. Three capacitors are connected as shown in the figure below with a battery of e.m.f 6V and zero internal resistance.
                                                               
                                    Figure 4
    Determine the voltage across 2µF capacitor. (3marks)
    
    SECTION B (55 MKS)
    Answer all questions in the spaces provided
12.  
    1. Define Total internal reflection. (1 mark)
    2. A ray of light makes a glancing angle of 60° with a flat glass surface as shown in the diagram below.
                                                                 
       Given that the critical angle is 42°, determine the angle of refraction r. (3marks)
    3. A point object X is located 3m in front of a pin- hole camera of length 30cm.
                                                            
                                         Figure 6
       Calculate the magnification of the object x. (3 marks)
    4. State two conditions necessary Total Internal reflection. (2 marks)
    5. State two areas total internal reflection can be applied. (2 marks)
13.  
    1. Study the diagram below on electromagnet and then answer the questions after it.
                                                                         
       1. Give a reason for winding the wire into a coil. (1 mark)
       2. State ways in which electromagnet can be made stronger. (2 marks)
    2. The figure below shows an electric bell
                                                 
       Briefly explain how it functions (3 marks)
    3. The Figure below shows an arrangement that may be used to investigate how electromagnetic force varies with current. Explain how the arrangement may be used for this investigation.  (3 marks)
                                                                
14.  
    1. The graph below shows a displacement versus time graph for a vibrating object. Use it to answer questions that follow.
                                                               
       1. Find the amplitude, period and frequency for the vibrating system. (4 marks)
       2. What is the displacement of the object at t = 0.3 s? (1 mark)
       3. Sketch in the same axis above, a graph of a wave which the frequency and amplitude are half of the wave in the figure above. (2 marks)
    2. Wambua strikes a steel super bridge with a hammer. If the speed of sound in steel is 5,200 m/s, determine the time taken for the sound to reach another Samuel 2.6 km far off the bridge with his ear on the rail. (3 marks)
    3. The figure below shows experiment to show the interference of waves
                                                            
       What is observed on the screen when the sizes of the slits are increased beyond the size of wavelength of waves produced by the light source. (1mark)
15.  
    1. State the purpose of manganese (iv) oxide in a dry cell. (1mark)
    2. Figure 4 below shows an electric circuit.
                                              
       1. Determine the resistance of the circuit (3 marks)
       2. What is the ammeter reading? (2 marks)
       3. Calculate
          1. The current through 2Ω resistor (2 marks)
          2. Hence or otherwise determine the potential difference across the 2Ω resistor. (2 marks)
16.  
    1. Define the following terms as used in curved mirrors.
       1. Principal focus, F (1 mark)
       2. Focal length, f (1 mark)
    2.  
       1. By use of a ray diagram, show how a concave mirror may be a dentist mirror  (3 marks)
       2. State two characteristics of the image formed. (2 marks)
    3. You are provided with the following apparatus; a white screen, metre rule and concave mirror. Using the apparatus, describe an approximate method of determining the focal length of the mirror. (3 marks)
    4. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image. (3 marks)

                                                                                        MARKING SCHEME

SECTION A : (25 Marks)

Answer all questions

1. The figure 2 below shows two plane mirrors inclined at an angle X from each other. A viewer counts a total of seven images from looking directly from each of the object O. Determine the value of X.  (3 marks)
                                                                              
                  n = 360 − 1 √1
                          θ
                   7 = 360 − 1√1
                           θ
                   θ  = 360 = 45°√1
                             8
2. Two pins are hanging from a magnet as shown in the diagram below.
                                                                                
   Explain why they do not hang vertically downwards.     (2 marks)
   • The pins acquire similar poles when magnetised by induction√1
   • They repel . √1
3. State two similarities of images formed by a plane mirror and a convex mirror. (2 marks)
   • Both images are upright/ erect√1
   • Both images are virtual /form behind the mirror√1
4. State the two Laws of refraction (2 marks)
   • The incident ray, the refracted ray and the normal at the point of incidence all lie at on the same plane. √1
   • The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media√1
5. Calculate the angle of refraction for a ray of light from air striking an air-glass interface, making an angle of 60° with the interface. (_an_g = 1.5) (2 marks
                              <i=30°
                          n = sinsini
                                sinsin r
                          sin sin r = sinsin 30° √1√1
                                                1.5 
                          r = sin^-1 (0.333)=19.47°√1
6. A student was investigating the brightness of bulbs when set up in different circuits. He used identical bulbs and cells. He set up circuits A and B as shown in figure (A) and (B) below.
                                                                  
                                                                                      A                                                    B
   State and explain which set up had the bulbs light brightest. (2 marks)
   • Set up B. √1
   • Cells in series give a higher e.m.f and bulbs in parallel offer least resistance hence higher current flows and bulbs light brighter. √1
7. A radio signal of 30MHz is received by an aerial whose length is 1/8 ^th of its wavelength. If the speed of light is 3.0 x 10⁸ m/s determine the length of the aerial. (3 marks)
                                    C = fλ
                         3×108 = (30×106)×λ√1
                                  λ = 10m√1
                     Areial = ¹/₈×10m=1.25m√1
8. A boy stood 3m from a large concave mirror of focal length 5m. State two characteristics of his image. (2 marks)
   • Image forms behind the mirror/ is virtual√1
   • Image is upright/ erect√1
   • Image is magnified√1
9. State two characteristics of sound waves. (2 marks)
   • Are mechanical/ require material medium for propagation. √1
   • Can be reflected, refracted and diffracted√1
10.  A negatively charged object was brought near a charged electroscope. The leaf was observed to fall then rose.
    1. State the charge of the electroscope
       • POSITIVE√1 (1 mark)
    2. Compare the magnitude of charge of the object with that of the electroscope.(1 mark)
       • The magnitude of the charge on the object was greater than charge on the electroscope√1
11. Three capacitors are connected as shown in the figure below with a battery of e.m.f 6V and zero internal resistance.
                                                                                        
    Determine the voltage across 2µF capacitor. (3marks)
                                 1/_CT= ¹/₁₂ +¹/₃ = ⁵/₁₂
                                   C_T= 2.4μF√1
                                 Q = CV = 2.4×6 = 14.4μC√1
                                 V = ^Q/_C = ^14.4/₃ = 4.8V√1
    
    SECTION B (55 MKS)
    Answer all questions in the spaces provided
12.  
    1. Define Total internal reflection. (1 mark)
       • Total internal reflection refers to the complete bouncing off of light at the boundary between two media in the optically denser medium. √1
    2. A ray of light makes a glancing angle of 60^o with a flat glass surface as shown in the diagram below.
                                                                      
       Given that the critical angle is 42°, determine the angle of refraction r. (3marks)
       n = 1/sin c = 1/sin 42 = 1/0.6691 = 1.4945√1
       n = ^{sin i}/_{sin r}, 1.4945 = ^{sin 30}/_{sin r√1}
       r = sin^-1 (^0.5/_1.4945) = 19.5482°√1
    3. A point object X is located 3m in front of a pin- hole camera of length 30cm.
                                                          
                                                    0
       Calculate the magnification of the object x. (3 marks)
       Magnifiation m, =  image distance ,v
                                    object distance .u√1
                                =  30cm√1 = 0.1√1
                                   300cm
    4. State two conditions necessary Total Internal reflection. (2 marks)
       • Angle of incidence in the optically dense medium should exceed critical angle. √1
       • Ray of light must be travelling from an optically denser medium to an optically less dense medium/ rarer medium. √1
    5. State two areas total internal reflection can be applied. (2 marks)
       • In communication using optical fibre. √1
       • In construction of prism binoculars. √1
       • In periscopes. √1
       • In making endoscopes used in medicine for viewing internal body organs. . √1
13.  
    1. Study the diagram below on electromagnet and then answer the questions after it.
                                                                 
       1. Give a reason for winding the wire into a coil. (1 mark)
          • Increase number of turns to increase strength of electromagnet. . √1
       2. State ways in which electromagnet can be made stronger. (2 marks)
          • Increasing magnitude of current. √1
          • Changing shape of core to u-shaped/ horse shoe shape. √1
          • Using a longer solenoid/coil. √1
          • Increasing the number of turns in the coil. √1
    2. The figure below shows an electric bell
                                                                   
       Briefly explain how it functions (3 marks)
       • When the switch is on, the current flows .The electromagnet becomes magnetized and hence attracts the soft-iron armature and at the same time pulls the hammer to strike the gong. √1
       • As the hammer moves towards the gong, the circuit is broken. The current stops flowing and the electromagnet loses its magnetism. This causes the spring to pull back the armature and reconnect the circuit again. √1
       • When the circuit is connected, the electromagnet regains its magnetism, pulls the armature ,hence the hammer strikes the gong again. This cycle repeats and the bell rings continuously√1
    3. The Figure below shows an arrangement that may be used to investigate how electromagnetic force varies with current. Explain how the arrangement may be used for this investigation.   (3 marks)
                                                            
       • The current will be varied incrementally and the value of current recorded. √1
       • The corresponding force/ reading on the spring balance for each value of current will be recorded as well. √1
       • A graph of current and its corresponding magnetic force will be plotted to establish this relationship. √1
14.  
    1. The graph below shows a displacement versus time graph for a vibrating object. Use it to answer questions that follow.
                                                                            
       1. Find the amplitude, period and frequency for the vibrating system. (4 marks)
                       Amplitude = 10cm√1
                       Period = 0.4 seconds√1
                       Frequency = 10.4 = 2.5Hz√2
       2. What is the displacement of the object at t = 0.3 s? (1 mark)
          • -10cm√1 (shown on graph)
       3. Sketch in the same axis above, a graph of a wave which the frequency and amplitude are half of the wave in the figure above. (2 marks)
    2. Wambua strikes a steel super bridge with a hammer. If the speed of sound in steel is 5,200 m/s, determine the time taken for the sound to reach another Samuel 2.6 km far off the bridge with his ear on the rail. (3 marks)
                                  Time = ^distance/_velocity√1 = ²⁶⁰⁰/₅₂₀₀√1 = 0.5s√1
    3. The figure below shows experiment to show the interference of waves
                                                               
       What is observed on the screen when the sizes of the slits are increased beyond the size of wavelength of waves produced by the light source. (1mark)
       • The waves pass through without being diffracted√1
                     Or
       • The waves pass through as plane waves√1
15.  
    1. State the purpose of manganese (iv) oxide in a dry cell. (1mark)
       • It acts as a depolarizer √1
    2. Figure 4 below shows an electric circuit.
                                                          
       1. Determine the resistance of the circuit (3 marks)
                   Resistors in parallel = ¹/₃ + ¹/₂ = ⁵/₆ = 0.8333 √1
                   Total resistance = 0.8333 + 0.8 √1
                                                1.6333 √1
       2. What is the ammeter reading? (2 marks)
                   I = ^V/_R √1 = ⁵/_1.633 = 3.0633A √1
       3. Calculate
          1. The current through 2Ω resistor (2 marks)
             V = 3.0613×0.833 = 2.55V √1
             I = ^V/_R = ^2.55/₂ = 1.276 = A √1
          2. Hence or otherwise determine the potential difference across the 2Ω resistor.  (2 marks)
             V = 3.0613×0.833 = 2.55V √2
                 Or
             5 − 2.448 = 2.552 V√2
16.  
    1. Define the following terms as used in curved mirrors.
       1. Principal focus, F (1 mark)
          • Point at which all rays parallel and close to the principal axis converge
                   Or
          • Point at which all rays parallel and close to the axis appear to diverge from after reflection √1
       2. Focal length, f (1 mark)
          • Distance from the pole of the mirror to its principal focus √1
    2.  
       1. By use of a ray diagram, show how a concave mirror may be a dentist mirror.   (3 marks)
          • Award for; √1 Correct object position (between P and F ) of mirror and correct mirror sign
          • √1-Correct rays that must be arrowed
          • √1 -Correct image position ( behind mirror, magnified)
       2.  State two characteristics of the image formed. (2 marks)
          • Image is upright/ erect √1
          • Magnified √1
          • Virtual/ forms behind the mirror √1
    3. You are provided with the following apparatus; a white screen, metre rule and concave mirror. Using the apparatus, describe an approximate method of determining the focal length of the mirror. (3 marks)
       • Using the mirror, focus a distant object on the screen √1
       • Adjust the distance between the screen and the mirror to obtain a sharp image. √1
       • Measure distance between screen and mirror. This is the focal length √1
    4. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image. (3 marks)
                         ¹/_f = ¹/_u + ¹/_v √1
                         1 − 15 = ¹/₁₀ + ¹/_v
                         1/v = − 6cm √1
                         v = − 6cm
       • The image is virtual / formed behind the mirror √1