Free KCSE Physics Topical Questions KNEC Standards

K.C.S.E Physics Q & A - MODEL 2008PP2QN19

16/7/2020

K.C.S.E Physics Q & A - MODEL 2008PP2QN19

(a) X- rays are used for detecting cracks inside metal beams
(i) State the type of the X- rays used
(ii) Give a reason for your answer in (i) above
(b) Figure 13 shows the features of an X- ray tube

(i) Name the parts labeled A and B
A
B
(ii) Explain how a change in the potential across PQ changes the intensity of the X- rays produced in the tube.
(iii) During the operation of the tube, the target becomes very hot. Explain how this heat is caused
(iv) What property of lead makes it suitable for use as shielding material?
(c) In a certain X- ray tube, the electrons are accelerated by a Pd of 12000V. Assuming all the energy goes to produce X- rays, determine the frequency of the X- rays produced. (Plank's constant h= 6.62 x 10,^-34 Js and charge on an electron, e = 1.6 x 10^-19C).

answers

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K.C.S.E Physics Q & A - MODEL 2008PP2QN18

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN18

(a) Figure 12 shows two circuits close to each other

When the switch is closed, the galvanometer shows a reading and then returns to zero. When the switch is then opened, the galvanometer shows a reading in the opposite direction and then returns to zero. Explain these observations.
(b) Explain how energy losses in a transformer are reduced by having:
(i) A soft- iron core
(ii) A laminated core
(c) An ideal transformer has 2000 turns in the primary circuit and 200 turns in the secondary circuit. When the primary circuit is connected to a 400V a.c. source, the power delivered to a resistor in the secondary circuit is found to be 800W. Determine the current in:
(i) The secondary circuit
(ii) The primary circuit

answers

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K.C.S.E Physics Q & A - MODEL 2008PP2QN17

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN17

(a) Three resistors of resistance 2.0 ohms, 4.0 ohms and 6.0 ohms are connected together in a circuit.
Draw a circuit diagram to show the arrangement of the resistor which
Gives
(i) Effective resistance of 3.0 ohms
(ii) Minimum resistance
(b) In figure 11 the voltmeter reads 2.1 V when the switch is open. When the switch is closed, the voltmeter reads 1.8 V and the ammeter reads 0.1A.

Determine:
(i) The e.m.f of the cell
(ii) The internal resistance of the cell
(iii) The resistance of the lamp

answers

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K.C.S.E Physics Q & A - MODEL 2008PP2QN16

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN16

(a) State two conditions necessary for total internal reflection to occur
(b) Figure 9 shows a ray of light incident on the boundary between two media 1 and at an angle

Show that the refractive index for a ray of light traveling from medium 1 to medium 2 is given by:
M2 = 1/Sin θ
(c) Figure 10 shows a ray of light incident on one face of a block of ice of refractive index 1. 31 and totally reflected at the adjacent face

Determine
(i) Angle Φ
(ii) Angle x
(iii) Angle θ, the greatest angle for which the total internal reflection is possible

answers

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K.C.S.E Physics Q & A - MODEL 2008PP2QN15

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN15

a) State one factor that affects the speed of sound in a solid.
b) An observer stands half-way between two vertical cliffs that are L metres apart. He moves directly towards one cliff and after a distance x=10cm from the centre, he strikes a gong and measures the time interval, t, between the echoes heard from the two cliffs. He moves a further 10m and again strikes the gong and measure the time interval between the echoes. The process is repeated several times. The graph in Figure 8 shows the relation between the time interval, t and the distance, x from the centre.

(i) From the graph, determine the value of x for which the time interval was 0.55.
(ii) Given that t= 4/vx where v is the speed of sound in air, determine the value of v from the graph
. (iii) If the maximum time measured by the observer was t=4.7s, determine the distance L between the cliffs.
(c) A search boat uses a signal of frequency 6.0 x 10⁴ Hz to detect a sunken ship directly below. Two reflected signals are received; one after 0.1 seconds from sunken boat and the other after 0.14 seconds from the sea bed. If the sea bed is 98 m below the boat, determine:
(i) The speed of the signal in water.
You may use the value of v from (ii) above.
(ii) The depth of the sunken ship below the boat

answers

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K.C.S.E Physics Q & A - MODEL 2008PP2QN14

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN14

A radioactive isotope of copper decays to form an isotope of Zinc as shown below

Name the radiation emitted and give a reason for your answer
Radiation
Reason

ANSWER

Beta particle
Gain of an electron OR
Mass number has not changed but atomic number has increased by 1
Atomic number has increased by one
Nature will not affect the speed

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The accelerating potential of a certain X-ray tube is increased. State the change observed on the X-rays produced.

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN13

The accelerating potential of a certain X-ray tube is increased. State the change observed on the X-rays produced.

ANSWER

Frequency increases
Becomes hard
Wavelength decreases
Strength / quality

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K.C.S.E Physics Q & A - MODEL 2008PP2QN12

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN12

A narrow beam of electrons in a cathode ray oscilloscope (CRO) strike the screen producing a spot. State what is observed on the screen if a low frequency a.c source is connected across the y-input of the CRO

ANSWER

Spot moves up and down

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K.C.S.E Physics Q & A - MODEL 2008PP2QN11

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN11

Figure 7 shows how rays from a distant and a near object are focused inside a human eye with a certain defect.

Name the defect and state the cause of this defect.
Defect
Cause of defect

ANSWER

Short sightedness/ myopia
Extended eyeball/ lens has short focal length/ eye ball too long any two

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A heating coil is rated 100W, 240V. At what rate would it dissipate energy if it is connected to a 220V supply?

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN10

A heating coil is rated 100W, 240V. At what rate would it dissipate energy if it is connected to a 220V supply?

answer

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K.C.S.E Physics Q & A - MODEL 2008PP2QN09

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN09

Figure 6 shows a circuit in which a battery of negligible internal resistance, two resistors, a capacitor, a voltmeter and a switch are connected.

Giving a reason for your answer in each case, state the reading of the voltammeter, V, when the switch is
(i) Open
V=…………………………
Reason…………………
(ii) Closed
V=…………………………
Reason……………….

answer

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K.C.S.E Physics Q & A - MODEL 2008PP2QN08

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN08

Figure 5 shows wavefronts approaching the boundary between two media.

The speed of the waves in medium (2) is higher than that in medium (1). On the same diagram complete the figure to show the wavefronts after crossing the boundary.

answer

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K.C.S.E Physics Q & A - MODEL 2008PP2QN07

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN07

Figure 4 shows a hack-saw blade clamped horizontally on a bench and the free end is made to vibrate about the rest position.

Determine the frequency of vibration of the blade.

answer

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K.C.S.E Physics Q & A - MODEL 2008PP2QN06

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN06

Figure 3 shows a flat spring made of iron clamped horizontally on the bench over a solenoid

When the switch is closed, the spring vibrates. Explain this observation.

answer

When the switch is closed, 1 flows the iron core in the solenoid is magnetized attracting the flat spring this causes a break in contact disconnecting current.
Magnetism is lost releasing the spring
Process is repeated (make and break circuit)

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K.C.S.E Physics Q & A - MODEL 2008PP2QN05

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN05

The diagram in figure 2 shows an object O placed in front of a converging lens. F and F are the principal foci for the lens.

The object is now moved along the principal axis until a virtual image is produced.
On the same diagram:
(i) Draw the object O in the new position along the principal axis;
(ii) Sketch rays to show formation of the virtual image

answer

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K.C.S.E Physics Q & A - MODEL 2008PP2QN04

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN04

An un-magnetized steel rod is clamped facing North-South direction and then hammered repeatedly for some time. When tested, it is found to be magnetized. Explain this observation

answer

Hammering causes the domains or dipoles to vibrate when setting, some domains
themselves in the N- S – direction due to the earth’s magnetic field causing magnetisation

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K.C.S.E Physics Q & A - MODEL 2008PP2QN03

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN03

You are provided with the following;
A cell and holder, a switch, a rheostat, an ammeter, a voltmeter and connecting wires. Draw a diagram for a circuit that could be used to investigate the variation of the potential difference across the cell with the current drawn from the cell.

answer

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K.C.S.E Physics Q & A - MODEL 2008PP2QN02

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN02

A leaf electroscope A is charged and placed on the bench. Another uncharged leaf electroscope B is placed on the same bench and moved close to A until the caps touch. State and explain what is observed on the leaves of A and B.

answer

Leaf in A falls a bit while leaf in B rises a bit
The two leaf electroscope share the charge

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K.C.S.E Physics Q & A - MODEL 2008PP2QN01

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN01

Figure 1 shows three point sources of light with an opaque object placed between them and the screen.

Explain the nature of the shadow formed along B and C.

answer

BC - Total absence of light; umbra, completely dark
- Total darkness
Rays are completed blocked from this region by the object

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K.C.S.E Physics Q & A - MODEL 2008PP1QN19

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP1QN19

a) State the principle of moments.
b) A uniform metal strip is 3.0cm wide, 0.6cm thick d 100cm long. The density of the metal is 2.7 g/cm3.
(i) Determine the weight of the strip.
The strip placed n a pivot and kept in equilibrium by forces as shown in fig. 13

(ii) Determine the value of F and R
(iii) X is the distance from the end of the plank to the point of application of force F. Force F is now applied at various points nearer to the pivot so that x increases. Equilibrium is maintained all the time. On the axes provided sketch the relation between force F and x.

(iv) Give a reason for the answer in (iii) above

answers

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K.C.S.E Physics Q & A - MODEL 2008PP1QN18

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP1QN18

(a) Define the term velocity ratio of a machine.
(b) Fig. 12 shows part of a hydraulic press. The plunger is the position where effort is applied while the Ram piston is the position where load is applied. The plunger has cross-section area, a m2 while the Ram piston has cross-section area, a m2.

When the plunger moves down a distance d the Ram piston moves up a distance D.
(i) State the property of liquid pressure on which the working of the hydraulic press works.
(ii) Derive an impression for the velocity ratio (V.R) in terms of A and a.
c) A machine of velocity ratio 45, overcomes a load of 4.5 x 103N when an effort of 135N is applied.
Determine:
(i) The mechanical advantage of the machine;
(ii) Efficiency of the machine;
(iii) The percentage of the work that goes to waste.

answers

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K.C.S.E Physics Q & A - MODEL 2008PP1QN17

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP1QN17

a) What is meant by absolute zero temperature?
Fig. 10 shows a set up to investigate the relationship between temperature and volume for a certain gas.

b) State two factors that are kept constant, in order to determine the relationship.
c) The graph in Fig. 11 shows the relationship between volume and temperature for the experiment.

(i) What was the volume of the gas at 0⁰C?
(ii) At what temperature would the volume of the gas be zero?
(iii) Explain why the temperature in part (ii) above cannot be achieved.
d) A sealed gas cylinder contains 300cm³ of certain gas at a temperature of 25⁰C, and at a pressure of 9.5x 10⁴pa. the gas in the cylinder was then cooled to 10⁰C.
Determine the new pressure of the gas in the cylinder.

answers

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K.C.S.E Physics Q & A - MODEL 2008PP1QN16

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP1QN16

a) Define the term heat capacity.
b) You are provided with the apparatus shown in Fig. 9 and a stop watch.

Describe an experiment to determine the specific latent heat of steam, l, using the set up. In your answer clearly explain the measurements to be made and how these measurements could be used to determine l.
c) A block of metal of mass 150g at 100⁰C is dropped into a lagged calorimeter of heat capacity 40JK^-1 containing 100g of water at 25⁰C. The temperature of the resulting mixture is 34⁰C. (Specific heat capacity of water=4200JK^-1).
Determine:
(i) Heat gained by calorimeter;
(ii) Heat gained by water;
(iii) Heat lost by the metal block;
(iv) Specific heat capacity of the metal block

answers

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K.C.S.E Physics Q & A - MODEL 2008PP1QN15

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP1QN15

a) State Newton's second law of motion.
b) A matatu starts from rest and accelerates to cover a distance of 49m in 7 seconds.
Determine
(i) Its acceleration;
(ii) Its velocity, after 7 seconds

c) A trolley moving on a horizontal bench of height 1.2m, strikes a barrier at the edge of the bench. The brass mass on the top of the trolley flies off on impact and lands on the ground 2.5m from the edge of the bench.
Determine:
(i) The time taken by the brass mass to reach the ground;
(ii) The speed at which the trolley struck the barrier.

answers

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K.C.S.E Physics Q & A - MODEL 2008PP1QN14

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP1QN14

The system in Fig. 8 is in equilibrium

When the temperature of the water is raised the system is observed to tilt to the right, state the reason for this observation.

answer

Heated water has lower density, hence lower up thrust

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K.C.S.E Physics Q & A - MODEL 2008PP2QN19

K.C.S.E Physics Q & A - MODEL 2008PP2QN18

K.C.S.E Physics Q & A - MODEL 2008PP2QN17

K.C.S.E Physics Q & A - MODEL 2008PP2QN16

K.C.S.E Physics Q & A - MODEL 2008PP2QN15

K.C.S.E Physics Q & A - MODEL 2008PP2QN14

The accelerating potential of a certain X-ray tube is increased. State the change observed on the X-rays produced.

K.C.S.E Physics Q & A - MODEL 2008PP2QN12

K.C.S.E Physics Q & A - MODEL 2008PP2QN11

A heating coil is rated 100W, 240V. At what rate would it dissipate energy if it is connected to a 220V supply?

K.C.S.E Physics Q & A - MODEL 2008PP2QN09

K.C.S.E Physics Q & A - MODEL 2008PP2QN08

K.C.S.E Physics Q & A - MODEL 2008PP2QN07

K.C.S.E Physics Q & A - MODEL 2008PP2QN06

K.C.S.E Physics Q & A - MODEL 2008PP2QN05

K.C.S.E Physics Q & A - MODEL 2008PP2QN04

K.C.S.E Physics Q & A - MODEL 2008PP2QN03

K.C.S.E Physics Q & A - MODEL 2008PP2QN02

K.C.S.E Physics Q & A - MODEL 2008PP2QN01

K.C.S.E Physics Q & A - MODEL 2008PP1QN19

K.C.S.E Physics Q & A - MODEL 2008PP1QN18

K.C.S.E Physics Q & A - MODEL 2008PP1QN17

K.C.S.E Physics Q & A - MODEL 2008PP1QN16

K.C.S.E Physics Q & A - MODEL 2008PP1QN15

K.C.S.E Physics Q & A - MODEL 2008PP1QN14

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