K.C.S.E Physics Q & A - MODEL 2016PP2QN12
.When germanium crystal is doped with arsenic, it becomes an N-type semiconductor. Explain how this change occurs.
(Number of electrons in the outermost shell for germanium =4, arsenic =5)
answer
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K.C.S.E Physics Q & A - MODEL 2016PP2QN10
Figure 6 shows a narrow beam of X-rays passing between two metal plates in air. The plates are connected in series with a switch, a cell and a milliameter.
It is observed that when the switch is closed a current flows in the milliameter. Explain this observation.
answer
K.C.S.E Physics Q & A - MODEL 2016PP2QN08
The following is part of radioactive decay series
Determine the values of a and b
answers
a = 234
b= 82 K.C.S.E Physics Q & A - MODEL 2016PP1QN17
(a) When a bus goes round a bend on a flat road, it experiences a centripetal force.
State what provides the centripetal force. (b) State the purpose of banking roads at bends.
(c)A student whirls a stone of mass 0.2 kg tied to a string of length 0.4 m in a vertical plane at a constant speed of 2 revolutions per second. (Take acceleration due to gravity g as 10 m/s2)
(i) State two forces acting on the stone when it is at the highest point. (ii) Determine the: (I)Angular velocity of the stone (II)Tension in the string when the stone is at the highest point; K.C.S.E Physics Q & A - MODEL 2015PP2QN16
(a) It is observed that alpha particles have a lower penetrating power than beta particles. Explain this observation.
(b) A radioactive substance has a half life of 12 years. Determine the time it would take to decay to 12.5% of its original value.
(c) A Geiger Müller (GM) tube is used for detecting radiations from a radioactive source.
State the function of: (i) the mica window; (ii) bromine gas in the tube. (d) (i) In a diffusion chamber, explain why some of the tracks formed are observed to be; (I) Short, (II) Straight. (ii) State two advantages of using a GM tube instead of a diffusion cloud chamber to detect radiations from radioactive substances.
answers
(a) Alpha particles are heavier and move at lower speeds hence less penetrating power than
Beta particles which are lighter and move faster
(c) (i) allows the radiations into the tube
(ii) absorbs kinetic energy of positive ions so that they do not cause secondary ionization in the tube (d) (i) Short - They ionize heavily loosing most of the energy hence cannot travel far. Straight - They are massive compared to air molecules hence collision with air molecules cannot change their path. (ii) GM is easily portable than a cloud chamber. GM is more sensitive. GM tube detects radiation at very low intensity and cloud chamber cannot detect radiation at very low intensity. K.C.S.E Physics Q & A - MODEL 2015PP2QN15
.(a) State two factors that determine the resistance of a metallic conductor.
(b) Explain how a fuse safeguards electrical appliances against excessive currents.
(c) A hair dryer is rated 2.5 kW, 240 V.
(i) Determine whether a 10 A fuse may be suitable for the hair dryer. (ii) Determine the cost of using the hair dryer for 3 hours if the cost of electricity is Ksh 0.80 per kilowatt hour. K.C.S.E Physics Q & A - MODEL 2015PP2QN12
Figure 4 shows a cathode ray entering into a region between two charged plates.
Complete the diagram to show the path of the ray in the field.
K.C.S.E Physics Q & A - MODEL 2015PP1QN18
(a) Figure 13 shows a pendulum bob suspended by a thread moving in a horizontal circle
(i) Name two forces acting on the pendulum bob as it moves.
(ii) State what happens to each of the forces when the angular velocity of the pendulum bob is increased. (iii) State two applications of uniform circular motion in daily life. (b) Figure 14 shows a block floating in water.
When the water is heated; it is observed that the block sinks further. Explain this observation.
answers
(a) (i) Tension (T)
Weight (Mg) (ii) Tension - increases Weight - remains constant (iii) Centrifuges Speed governors Merry-go-rounds (b) When heated the density of the water decreases hence block sinks further as it displaces more volume of water. K.C.S.E Physics Q & A - MODEL 2014PP2QN13The current of electrons hitting the screen of a cathode ray oscilloscope is 2.0 X 10-4A
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