The figure below shows the path of a ray of light passing through a rectangular glass block placed in air
Calculate the refractive index of glass (2mks)
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 Two capacitors of capacitance 2 μF 1μF are connected in parallel. A p.d of 3V is applied across them. Find the energy stored in the combination. (2mks)
The figure below shows an object placed in front of a concave mirror. By use of correct ray diagram, locate the position of image
Solution
The figure bellows shows a wave profile for a wave whose frequency is 2HZDetermine the value of t3(s) (2mks)
Solution
The figure below shows two parallel magnets with unlike poles adjacent to each other. Sketch the magnetic field pattern around the magnets (2mks)
Solution
(a) Define Radio-activity (2mks)
Radioactivity is the spontaneous disintegration of a nucleus releasing
alpha, beta and gamma radiations accompanied by the release of energy (b) When carrying out experiments with radioactive substances the source should never be held with bare hands but with forceps. Explain? (1mk)
Radioactive substances are harmful to body cells when ingested
(i) Plot on the graph paper provided the graph of the count rate (y-axis) against time
A graph of count Rate against time(s)
(ii) From the graph, determine the half-life of Radon-220 (1mk)
Half-life of radon 220=54 sec + 2 (showing on graph a must)
(e) The diagram in the figure below shows paths taken by three radiations A,B and C from a radioactive isotope through an electric field.
(i) State the charge on plate Y (1mk)
(ii) Identify the radiations A and C (2mks)
(iii) Give a reason why C deviates more than A (1mk)
C more massive than A
(a) A 240v mains transformer has 800 turns in the primary and N turns in the secondary. It is used to supply energy to a 12v/21w lamp. (i) Calculate the number of turns in the secondary (2mks)(ii) What is the efficiency of the transformer if the current drawn from the 240V mains is 100mA (2mks)
The circuit above shows a step-down transformer used to light a lamp of resistance.
Calculate.(i) the reading of voltmeter, V, with, S, open (2mks)(ii) the reading of the ammeter A with S closed (neglect the effective resistance of the secondary winding) (2mks)(iii) the power dissipated in the lamp (2mks)(iv) the primary current if the transformer is 90% efficient (3mks)
(a) State two advantages of a C.R.O as a voltmeter
(b) A television tube is a cathode ray tube modified. State two modifications
(c) State the functions of the following parts of a C.R.O(i) Grid
(ii) X-plates
(iii) Fluorescent screen
(d) A modern X-ray tube is shown below
(i) Name the parts labeled A-D (2mks)A
Copper Anode
B
Tungsten Target
C
Filament
D
Cooling fins
(ii) Give the functions of:- (1mk)(i) Shielding with lead
Lead absorbs the radiation (1mk)
(ii) Evacuating the tube
Prevents collisions, avoid secondary electrons (1mk)
(a) Define doping (1mk)
Process of introducing foreign element (impurity) into a pure semi-conductor,
(b) Distinguish between a p-type and n-type semi conductors (2mks)
(c) Using a diagram illustrate a forward P-N junction (2mks)(d) The figure below shows a bridge circuit
A capacitor has been connected across the resistor as shown
(i) Sketch of the figure below the wave form when a CRO is connected across the resistor, R
(ii) On the same axes, sketch a wave form when C.R.O is connected across R when the capacitor has been removed (1mk)
(a) Explain why bulbs in along corridor are not wired in series (2mks)
(b) An electric cooker has an oven rated 2500w, a grill rated 1500w and two plates each of 1000W. This cooker operates directly from 240v supply. What is the costs of operating all the parts at once for 30 minutes if electricity costs sh.10.00 per unit? (3mks)
(c) Study the figure below
(i) What name is given to the fitting in the diagram (1mk)
3 pin plug
(ii) Identify the parts labeled (2mks)A
Neutral wire
B
Earth wire
C
Live wire
D
Fuse
Give two advantages of a circuit breaker instead of a fuse in domestic wiring (2mks)
State the conditions for generation of e.m.f from a magnet (2mks)
The following is a part of a radio-active series
Identify the radiation r, find the values of c and d (3mks)r
r is βeta particle
c
c is 206
d
d is 82
State two uses of optical fibres whose working relies on total internal reflection (2mks)
Give a reason why gases are poor transmitters of sound (1mk)
Molecules in gases are much further apart
Other than penetrating powers, state two differences between soft and hard X-rays (2mks)
Two mirrors are inclined at 60o to each as shown:
Complete the ray diagram to show how it travels after striking the two mirrors and find the angle of reflection on each surface (2mks)Solution
K.C.S.E Physics Q & A - MODEL 2019PP2QN19
​(a) Define half life as used in radioactivity.
(b) Figure 13 shows a device used to detect radioactivity by forming tracks when air is ionised. 
(i) State the name of the device shown.
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