Physics Paper 2 Questions and Answers - Form 4 Term 1 Opener Exams 2021

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PHYSICS
PAPER 2
(THEORY)
FORM 4 TERM 1 OPENER EXAMS
TIME: 2 HOURS

INSTRUCTIONS TO CANDIDATES

Answer all the questions in the spaces provided.
Mathematical tables and electronic calculators may be used.
All workings must be clearly shown where necessary.
Take g=10N/kg

SECTION A (25MARKS)
Answer all the questions

Figure1 below shows two mirrors M1 and M2 are inclined at right angles to each other.

Trace the reflection of the ray through the two mirrors and find the angle between the incident ray and reflected ray of mirror M2. (2mks)
State the reasons why a convex mirror is preferred over a plane mirror for use as a driving mirror. (1mk)
A current of 0.5A flows in a circuit. Determine the quantity of charge that crosses a point in 4 minutes through the circuit. (2mks)
A radio station broadcasts on a wavelength of 150m at a frequency of 200 kHz. Calculate the velocity of the radio waves. (2mks)
The internal resistance of the cell in the figure below is 0.5 Ω.

Determine the ammeter reading when the switch S is closed. (2mks)
A man standing 400 away from a wall bangs two pieces of wood together and hears an echo 2.5 seconds later. Determine the speed of sound in air at that place. (2mks)
State the property of light associated with formation of shadows. (1 mark)
In the circuit diagram shown in figure 3 the lamps are identical and cells are also identical.

State with a reason, in which circuit the lamp will be lit for a longer period. (2 marks)
Explain in terms of domain theory, what happens when a bar magnet is placed in a solenoid in which an alternating current flows. (2 marks)
Use appropriate rays to complete the ray diagram in figure 4 and state the position of the object formed. (3 marks)
Figure 5.0 shows a transverse wave.
1. Calculate the frequency of the wave. (2 marks)
2. Sketch another wave on the same diagram that has double the frequency and half the amplitude and label it as M. (1 mark)
The figure 6.0 below shows a network of capacitors.

Determine the combined capacitance of the network. (2 marks)

SECTION B( 55MARKS)

1. The figure below shows a ray of green light through a prism. The speed of green light in the prism is 2.0 x 108m/s
  1. Determine the refractive index of the prism material( speed of light in air = 3.0 x 108m/s (3mks)
  2. Given the r ==23.20, determine the angle Ѳ (3mks)
2. The diagram below show two prisms
  
  Given that the critical angle of the glass in both prisms is 420 sketch the paths of the two rays in each prism indicating all the angles. (2mks)
  1. Give two application of total internal reflection (2mks)
1. What is meant by the term capacitance? (1mk)
2. The figure below shows a point placed near a positively charged rod.
  Draw on the diagram the resulting electric field patterns. (1mk)
3. When a positively charged conductor is brought close to a candle, the flame is diverted as shown in the figure below. Explain this observation. (2mks)
4. The figure below shows three capacitors of capacitance 3µF, 2µF, and 6µF. Connected to a 12v supply circuit.
  
  Calculate:
  1. The total capacitance of the circuit. (3mks)
  2. The total charge stored in the circuit. (3mks)
  3. The potential differences across 2µF capacitor. (2mks)
1. Explain how sound reaches our ears. (2 marks)
2. State two characteristics of sound waves. (2 marks)
3. 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. (2 marks)
4. A boy whistles once at a distance 250 m from a vertical cliff. If the temperature in the surrounding is 50C .If the speed of sound = (331.5m/s at 00c) the speed in air increases at about 0.6 m/s per 0C,
  1. Determine the distance travelled by sound. (2 marks)
  2. Determine the speed travelled at 50C. (2 marks)
  3. Calculate the time taken for the boy to hear the echo. (2 marks)
1. Define electric current (1mks)
2. The figure below shows an electric circuit with two bulbs B1 and B2 which are identical.
  
  Explain what happens to the bulbs when
  1. S₁ only is closed (2mks)
  2. S₁ and S₂ are closed (2mks)
3. The figure below shows an electric circuit. Use the circuit to determine the current supplied by the battery (3mks)
1. Figure 14 below shows a series of wave fronts one wavelength apart approaching a gap between barriers in ripple tank.
  
  On the same diagram, show what happens when the waves pass through the gap. (1 mark)
2. Some plane water waves were produced in a ripple tank. They pass from a region of deep water into a region of shallow water. Figure 15.0 shows what the waves look like from above.
  
  State what happens at the boundary to
  1. the frequency of the waves (1 mark)
  2. the speed of the waves (1 mark)
  3. the wavelength of the waves (1 mark)
1. State three factors that affect the strength of an electromagnet. (3marks)
2. In the set up below, the suspended metre rule is in equilibrium balanced by the magnet and the weight shown. The iron core is fixed to the bench:
  1. State and explain the effect on the metre rule when the switch S, is closed.(2marks)
  2. What would be the effect of reversing the battery terminals? (1mark)
3. The figure below shows two parallel current carrying conductors A and B placed close to each other. The direction of the current is into the plane of the paper.
  
  On the same figure;
  1. Sketch the magnetic field pattern. (1mark)
  2. Indicate the force F due to the current on each conductor. (1mark)

MARKING SCHEME

SECTION A (25MARKS)
Answer all the questions

Figure1 below shows two mirrors M1 and M2 are inclined at right angles to each other.

Trace the reflection of the ray through the two mirrors and find the angle between the incident ray and reflected ray of mirror M2. (2mks)

Gives a wide field of view
State the reasons why a convex mirror is preferred over a plane mirror for use as a driving mirror. (1mk)
Q= It
= 0.5 x 4 x 60√
= 120C√
A current of 0.5A flows in a circuit. Determine the quantity of charge that crosses a point in 4 minutes through the circuit. (2mks)
v= λf
= 150 x 200 x 1000
= 30,000,000
=3.0 x 10⁷ m/s√
A radio station broadcasts on a wavelength of 150m at a frequency of 200 kHz. Calculate the velocity of the radio waves. (2mks)
The internal resistance of the cell in the figure below is 0.5 Ω.

Determine the ammeter reading when the switch S is closed. (2mks)
E = IR
2= 2I +0.5 I√
2=⁵/₂ I
I = 0.8 A√
A man standing 400 away from a wall bangs two pieces of wood together and hears an echo 2.5 seconds later. Determine the speed of sound in air at that place. (2mks)
Speed = ^2d/_t
= 2 x 400
2.5
= 320m/s.
State the property of light associated with formation of shadows. (1 mark)
Light travels in a straight line. Rectilinear propagation of light
In the circuit diagram shown in figure 3 the lamps are identical and cells are also identical.

State with a reason, in which circuit the lamp will be lit for a longer period. (2 marks)
Circuit A
The cells in A are in parallel, current drawn from each cell in less than in B
or
Effective internal resistance in circuit A is less than in B
Explain in terms of domain theory, what happens when a bar magnet is placed in a solenoid in which an alternating current flows. (2 marks)
Alternating current disarranges / disorients / upsets the alignment of the dipoles in the domains causing dipoles to lose the alignment
Use appropriate rays to complete the ray diagram in figure 4 and state the position of the object formed. (3 marks)

Ans

Correct rays = 2mks
Nature of the object
Image is real
Figure 5.0 shows a transverse wave.
1. Calculate the frequency of the wave. (2 marks)
  f = 1
  T
  = 1
  0.12
  = 8.333 Hz
2. Sketch another wave on the same diagram that has double the frequency and half the amplitude and label it as M. (1 mark)
  
  New f = 16.666
  A = 1
The figure 6.0 below shows a network of capacitors.

Determine the combined capacitance of the network. (2 marks)
For series ¹/_Cs= ¹/₃ + ¹/₁= 1 + 3 =⁴/₃
3
C_s = ³/₄ = 0.75µF
for parallel : C_e = (2 + 0.75)µF
= 2.75µF

SECTION B( 55MARKS)

1. The figure below shows a ray of green light through a prism. The speed of green light in the prism is 2.0 x 108m/s
  1. Determine the refractive index of the prism material( speed of light in air = 3.0 x 108m/s (3mks)
  2. Given the r ==23.20, determine the angle Ѳ (3mks)
2. The diagram below show two prisms
  
  Given that the critical angle of the glass in both prisms is 420 sketch the paths of the two rays in each prism indicating all the angles. (2mks)
  1. Give two application of total internal reflection (2mks)
    Periscope
    Prism binoculars
    Optical fibre
1. What is meant by the term capacitance? (1mk)
  Its charge stored per unit voltage.
2. The figure below shows a point placed near a positively charged rod.
  Draw on the diagram the resulting electric field patterns. (1mk)
  
  Ans
3. When a positively charged conductor is brought close to a candle, the flame is diverted as shown in the figure below. Explain this observation. (2mks)
  
  The higher concentration of positive charges at sharp end of the conductor causes ionization of the surrounding air√ to produce electrons and positive ions. Electrons are attracted towards the conductor while heavy positive ions drift away diverting the part of the flame.√
4. The figure below shows three capacitors of capacitance 3µF, 2µF, and 6µF. Connected to a 12v supply circuit.
  
  Calculate:
  1. The total capacitance of the circuit. (3mks)
    C_P=2+6=8µf√
    C_T=3x8 = 24 = 2.18 µf.√
    3+8 11
  2. The total charge stored in the circuit. (3mks)
    Q =CV √
    = 2.18 X 10^-6 X 12√
    = 2.616 X 10^-5 C√
  3. The potential differences across 2µF capacitor. (2mks)
    p.d across 2 µf = 2.616 x 10^-6√
    8 x 10^-6√
    = 3.27V √
1. Explain how sound reaches our ears. (2 marks)
  Sound is a form of energy and it comes from vibrations. √These vibrations create sound waves which move through mediums√ such as air and water before reaching our ears.
2. State two characteristics of sound waves. (2 marks)
  Loudness
  Pitch.
  Timbre or quality
  Frequency and pitch
  Fundamental tones and harmonics
3. 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. (2 marks)
  Time taken = distance / speed = ²⁶⁰⁰/₅₂₀₀ =0.50 seconds√√
4. A boy whistles once at a distance 250 m from a vertical cliff. If the temperature in the surrounding is 50C .If the speed of sound = (331.5m/s at 00c) the speed in air increases at about 0.6 m/s per 0C,
  1. Determine the distance travelled by sound. (2 marks)
    Distance travelled = 2d = 250 x2 =500m
  2. Determine the speed travelled at 50C. (2 marks)
    Speed at 5ºC = 331.5+ (0.6 × 5) = 334.5m/s
  3. Calculate the time taken for the boy to hear the echo. (2 marks)
    Time taken = ^distance/_speed = ⁵⁰⁰/_334.5
1. Define electric current (1mks)
  rate of flow of change
2. The figure below shows an electric circuit with two bulbs B1 and B2 which are identical.
  
  Explain what happens to the bulbs when
  1. S₁ only is closed (2mks)
    Both bulbs light with the same brightness – they receive the same amount of current
  2. S₁ and S₂ are closed (2mks)
    Only bulb B1 light. Bulb B2 is short circuited
3. The figure below shows an electric circuit. Use the circuit to determine the current supplied by the battery (3mks)
1. Figure 14 below shows a series of wave fronts one wavelength apart approaching a gap between barriers in ripple tank.
  
  On the same diagram, show what happens when the waves pass through the gap. (1 mark)
2. Some plane water waves were produced in a ripple tank. They pass from a region of deep water into a region of shallow water. Figure 15.0 shows what the waves look like from above.
  
  State what happens at the boundary to
  1. the frequency of the waves (1 mark)
    Frequency not affected
  2. the speed of the waves (1 mark)
    Speed reduces
  3. the wavelength of the waves (1 mark)
    Wavelength reduces
1. State three factors that affect the strength of an electromagnet. (3marks)
  Amount of current.✓
  Number of turns in a coil ✓
  Shape of the core ✓
2. In the set up below, the suspended metre rule is in equilibrium balanced by the magnet and the weight shown. The iron core is fixed to the bench:
  1. State and explain the effect on the metre rule when the switch S, is closed.(2marks)
    The magnet will be attracted ✓① towards the soft iron core.
    The end of the coil facing the magnet becomes South Pole when switch is closed; and the rule turns anticlockwise ✓①
  2. What would be the effect of reversing the battery terminals? (1mark)
    The polarities of the electro-magnet becomes reversed therefore the magnet is now repelled away from iron core ; and the rule turns clockwise ✓①
3. The figure below shows two parallel current carrying conductors A and B placed close to each other. The direction of the current is into the plane of the paper.
  
  On the same figure;
  1. Sketch the magnetic field pattern. (1mark)
  2. Indicate the force F due to the current on each conductor. (1mark)