FORM FOUR PHYSICS NECTA 2021

THE UNITED REPUBLIC OF TANZANIA NATIONAL EXAMINATIONS COUNCIL OF TANZANIA

CERTIFICATE OF SECONDARY EDUCATION EXAMINATION

031/1 PHYSICS 1

(For Both School and Private Candidates)

Time: 3 Hours Year: 2021

Instructions

l . This paper consists of sections A, B and C with a total of eleven (11) questions.

2. Answer all questions in sections A and B and two (2) questions from section C.

3. Section A carries fifteen (15) marks, section B sixty (60) marks and section C carries twenty five (25) marks.

4. Cellular phones and any unauthorized materials are not allowed in the examination room.

5. Non-programmable calculators and mathematical tables may be used.

7. Where necessary the following constants may be used:

(i) Acceleration due to gravity, g = 10 m/s-2

(ii) Density of water, p = 1000 kg/m3

(iii) Pie, 3.14.

(iv) Linear expansitivity of steel =  1.1 x 10-5K-1

SECTION A (15 Marks)

Answer all questions in this section.

1. For each of the items (i) - (x), choose the correct answer from among the given alternatives and write its letter beside the item number in the answer booklet provided. (10 marks)

(i) How can the density of a stone with mass X when in air and volume Y when fully immersed in water be found?

1. By dividing the reduced mass of the stone to the volume of the water displaced.
2. By dividing the mass of the stone in the air to the volume of the water displaced.
3. By dividing the apparent mass of the stone in the water to the volume of the water displaced.
4. By dividing the mass of the stone in air to the upthrust.
5. By dividing the apparent mass of the stone to the upthrust.

(ii) Which property of concave mirrors is suitable for a dentist to consider when selecting concave mirrors for repairing dental related activities?

1. The one that produce diminished images.
2. The one with wider field of view.
3. The one which produce virtual and erect image.
4. The one that produce larger magnification.
5. The one in which objects and images are seen easily.

(iii) Which one of the following is not a property of magnetic lines of force?

1. Are continuous and always form closed loops.
2. Start at the north pole and end at the south pole.
3. Never cross one another.
4. Enter or leave a magnetic material at right angles to the surface.
5. Pass through magnetic materials only.

(iv) Which velocity-time graph represents the ball thrown vertically upwards and returning ground? (v) Which statement describes the difference between maximum thermometer and minimum thermometer?

1. Maximum thermometer uses mercury while minimum thermometer uses alcohol.
2. Maximum thermometer measures the temperature of the solid object while minimum thermometer measures the temperature of the liquid.
3. Maximum thermometer measures the temperature in Kelvin while minimum thermometer measures the temperature in degree centigrade.
4. Maximum thermometer has concave meniscus while minimum thermometer has convex meniscus.
5. Maximum thermometer has index below the meniscus while minimum thermometer has index above the meniscus.

(vi) Choose the properties which correctly describe the hydroelectric energy from the following properties.

(1) Energy is virtual available

(2) Not reliable

(3) Environmental friendly

(4) Turn turbine to drive generators

1. (2), (3) and (4)
2. (1), (2) and (4)
3. (1), (3) and (4)
4. (2), (3) and (4)
5. (1) , (2) and (3)

(vii) Why do people prefer white shawl to wrap around a baby to keep the baby warm?

1. White shawl is a poor conductor.
2. White shawl indicates cleanliness.
3. White shawl is the poor radiator.
4. White shawl has pockets of air trapped in it.
5. White shawl is a good reflector of heat.

(viii) Which statement about a wet-and-dry bulb hygrometer is correct?

1. Wet bulb thermometers measure the temperature of the surrounding air.
2. The temperature recorded by a wet-bulb thermometer is always larger than that recorded by a dry-bulb thermometer.
3. When the difference in temperature recorded by wet and dry-bulbs is larger no water evaporates.
4. The value of relative humidity is low when the temperature of wet and dry bulbs is the same.
5. Wet-bulb is cooled by the process of evaporation of water.

(ix) The following diagram shows a cathode ray oscilloscope. Which conditional change on the oscilloscope can lead into producing a brighter trace on the screen? 1. Using time-base and connect alternating voltage to Y-plates
2. Increasing the anode voltage
3. Switching off time-base and connect battery to Y-plates
4. Switching off time-base and connect alternating voltage to Y-plates
5. Using time base only

(x) Which statement distinguishes gravity from gravitational force?

1. Gravity is the force that pulls objects towards the earth while gravitational force is the attractive force existing between any two objects.
2. Gravity is the force of attraction between two objects while gravitational force is the force acting to pull objects toward the earth.
3. Gravity is sometimes called universal gravitation while gravitational force is also called centripental force.
4. Gravity is applicable from the largest stars to the smallest atoms while gravitational force does not.
5. E Gravity holds planets to revolve around the sun while gravitational force does not hold planets.

2. Match the functions of instruments in List A with their corresponding instruments in List B by writing the letter of the correct response beside the corresponding item number in the answer booklet provided. (5 marks)

 List A List B Helps to observe the behaviours of waves.  Discriminates sound waves based on frequency, amplitude and direction. Produces heat energy used to heat the food.  It is used to determine the resonance in an air column. Helps to study the properties of stationary waves. Resonance tube Guitar Turning folk Microwave oven The human ear Sonometer Ripple tank Radar

SECTION B (60 Marks)

Answer all questions in this section.

3. (a) With the help of diagram(s), describe how you would use a manometer to measure the pressure of a gas at a gas-tap. (6 marks)

(b) A uniform metal cube of length 5 m and mass 9 kg is suspended horizontally by two wires attached at 50 cm from the left end of the cube and 150 cm from the right end of the cube. What is the tension in each wire? (4 marks)

4. (a) With the aid of a diagram, show that when a plane mirror is rotated through an angle θ about an axis normal to the plane containing the incident ray and the normal, the reflected ray rotates through an angle 2 θ. (5 marks)

(b) A compound microscope consists of two lenses of focal length 12 cm and 6 cm for the objective lens and the eyepiece lens respectively. The two lenses are separated by a distance of 30 cm. The microscope is then focused to a point where the image is formed at infinity. Use a graphical method to determine the position of the first image. (5 marks)

5. (a) A water boiler containing 150 kg of water at a temperature of 200 C is connected to the 240 V power supply. Given that the resistance of the heating coil in the boiler is 25 Ω, how many kilowatt-hours of electrical energy will be consumed if the water in the boiler is heated to a temperature of 400 C? (5 marks)

(b) Use an appropriate diagram to describe the nature, effect on electric field and penetrating powers of alpha particles, beta particles and gamma rays. (5 marks)

6. (a) Suppose a force F acts on a body of mass m for time t causing its velocity to change from initial velocity u to final velocity v; Explain how the Newton's second law of motion can be used to define a unit of force of one Newton. (5 marks)

(b) The handle of a screw-jack is 35 cm and the pitch of a screw is 0.5 cm. If the efficiency of the jack is 55 % , calculate the force required to be applied at the end of the handle to lift a load of 2300 N. (5 marks)

7. (a) A part of a steel tape used by a surveyor is 9 m at 25 0 C. What is the overall length measured using this tape sixty seven times on a warm day corresponding to 38 0 C. (5 marks)

(b) A waterfall is 100 m high and the difference in temperature between the water at the top and that at the bottom is 0.24 K. Calculate the specific heat capacity of water. (5 marks)

8. (a) Briefly explain four effects of global warming. (6 marks)

(b) Why is it not advisable for soldiers to march across the bridge with the same beat? (4 marks)

SECTION C (25 Marks)

Answer two (2) questions from this section.

9. (a) (i) Draw a well labelled diagram of a dry cell. (4 marks)

(ii) How do the components of a dry cell differ from those of the Leclanche cell? (2 marks)

(b) You are provided with the following components and power supplies: Base power supply, VBB•, collector power supply, Vcc; n-p-n transistor; base resistor, RB', load resistor, RL and coupling capacitors Cl and C2 in the input and output circuits respectively. Draw a well labelled single-stage common-emitter (CE) amplifier circuit showing directions of currents. (6.5 marks)

10. (a) Explain the working principle of a transformer. (5.5 marks)

(b) Describe how diffraction of water waves takes place in narrow and wide gaps. (7 marks)

11. (a) A small house with mains supply of 240 V has two heaters each rated at 2.5 kW. The supply has a main fuse rated at 15 A. Show whether this fuse can support the operation of the two heaters at the same time. (4 marks)

(b) A simple a.c. generator produces a low e.m.f. Explain any three design alterations that you would make to the generator in order to convert it into one of higher e.m.f. (5.5 marks)

(c) You are given a chance of buying an electronic device that can be used to convert the generator in part I l (b) into one of higher e.m.f. Describe one device which you will choose to buy for the purpose. (3 marks)

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