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A transformer of 480 turns in the primary coil is used to connect a 9V a.c electric device to a 240V a.c mains supply. Calculate the number of turns in the secondary coil.
Date posted:
February 12, 2019
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A transformer in a welding machine supplies 6V from a 240V mains supply. If the current used in the welding is 30A. Determine the current in the mains.
Date posted:
February 12, 2019
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A body weighs 32N in kerosene and 30N in water. If the body weighs 40N in air, find the relative density of kerosene.
Date posted:
February 11, 2019
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Define angular displacement and state its unit.
Date posted:
February 10, 2019
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A certain transformer steps down mains supply from 240V to 6V. There are 1200 turns in the primary circuit. A bulb of 36W is connected to the secondary circuit. Given that the efficiency of the transformer is 100% determine:
a) The number of turns in the secondary circuit.
b) The current in the primary circuit.
Date posted:
February 6, 2019
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A metal block of density 7.8g/cm3 weighs 117N in air. Find the weight of the block when fully immersed in water of density 1.0g/cm3.
Date posted:
February 2, 2019
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a) An object of mass 0.60kg tied to the end of a rope is whirled in a horizontal circle of radius 2.0m with a constant speed of 10m/s. Find the tension in the string.
Date posted:
February 1, 2019
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What do you understand by the term angular velocity?
Deduce the relationship between the linear speed and angular velocity.
Date posted:
January 31, 2019
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An object floats in sea water of density 1.03x10^3kg/m^3. It displaces 260m^3 of sea water. Find the mass of the object.
Date posted:
January 30, 2019
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A sling of length 1m and holding a stone of mass 200g at its free end is whirled in a horizontal plane such that it completes 10 revolutions in 5 seconds. Determine:
a) Tension in the sling
b) The frequency of rotation
c) The velocity with which the stone clips off when released
Date posted:
January 30, 2019
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A particle revolves at 2Hz in a circle of radius 2m. Calculate its:
a) Linear speed
b) Angular velocity
Date posted:
January 29, 2019
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A bucket containing water is rotated in a vertical circle of radius 80cm. What should its velocity be so that the water may not spill out?
Date posted:
January 28, 2019
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Explain why an object Weighs more in air than when fully immersed in water.
Date posted:
January 21, 2019
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A spring supporting a weight of 30N extends by 1.5 cm. Determine the spring constant.
Date posted:
January 21, 2019
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A uniform plank of wood of length 5 m is pivoted at its centre. A girl of mass 32 kg sits at one end of the plank. Determine how far from the pivot a boy of mass 40 kg should sit in order to balance the plank.
Date posted:
January 21, 2019
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A screen is placed 80cm from an object. A lens is used to produce on the screen an image with a magnification of 3. What is the distance between the object and the lens? Calculate the focal length of that lens.
Date posted:
January 21, 2019
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A bullet is shot vertically upward and rises for a maximum height of 1000m. What is the initial velocity of the bullet and the total time of flight?
Date posted:
January 14, 2019
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Explain why during anomalous expansion of water, heat transfer is limited to conduction and radiation.
Date posted:
December 30, 2018
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State a reason why it may not be possible to suck a liquid into your mouth using drinking straw on the surface of the moon.
Date posted:
December 10, 2018
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State the reason why the speed of the water at the narrow section of a river is higher than at the wider section.
Date posted:
November 29, 2018
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Two vertical opposite forces act on a metre rule at the 10 cm and 60 cm mark respectively.if each of the forces has a magnitude of 2.4N. Calculate their moments on the metre rule about the 30 cm mark.
Date posted:
November 13, 2018
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Explain the applications of junction diodes.
Date posted:
October 18, 2018
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Explain the occurrence of forward bias of a p-n junction and reverse bias of a p-n junction.
Date posted:
October 18, 2018
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What are junction diodes?
Date posted:
October 18, 2018
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What is an intrinsic semiconductor?
Date posted:
October 18, 2018
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Define the following terms (i) Conductors (ii) Insulators (iii) Semiconductors
Date posted:
October 18, 2018
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Hazards of radioactivity and their precautions
Date posted:
October 17, 2018
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A radioactive element has an initial count rate of 2,400 counts per minute on a scaler. The count rate falls to 300 units per minute in 30 hours, (a) Calculate the half-life of the element (b) If the initial number of atoms in another sample of the same element is 6.0 × 1020, how many atoms will have decayed in 50 hours?
Date posted:
October 17, 2018
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The initial number of atoms in a sample is 5.12 × 1020. If the half-life of the sample is 3.0 seconds, determine the number of atoms that will have decayed after six seconds.
Date posted:
October 17, 2018
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An isotope has a half-life of 576 hours. Complete the following table and show how mass varies with time from an initial mass of 1280 g?
Time (hrs)----576--1152--1728---2304
Mass (g)-------640--x------y-----z
Date posted:
October 17, 2018