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In an X-ray tube it is observed that the intensity of X-rays increases when potential difference across the filament is increased. Explain this observation
Date posted:
February 20, 2017
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State the differences between hard X-ray and soft X-rays.
Date posted:
February 20, 2017
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State and explain the effect of increasing the E.H.T in an X-ray tube on the X-rays produced.
Date posted:
February 20, 2017
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Name two differences between cathode rays and electromagnetic radiations.
Date posted:
February 20, 2017
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State two differences between the cathode ray tube (CRT) of a T.V. and the cathode ray oscilloscope (CRO).
Date posted:
February 20, 2017
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A student electroplated a spoon with copper metal. Write an equation for the process that took place at the cathode.
Date posted:
February 18, 2017
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Hydrogen and oxygen can be obtained by electrolysis of acidified water. Using equations for the reactions at the electrodes, explain why the volume of hydrogen obtained is twice that of oxygen.
Date posted:
February 18, 2017
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A block of glass of mass 250 g floats in mercury. What volume of glass lies under the surface of the mercury? (Density of mercury is 13.6 x 103Kgm-3)
Date posted:
February 18, 2017
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A block of wood weighing 2.0 N is held under water by a string attached to the bottom of a container. The tension in the string is 0.5 N. Determine the density of the wood.
Date posted:
February 18, 2017
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A solid copper sphere will sink in water while a hollow copper sphere of the same mass may float. Explain this observation.
Date posted:
February 18, 2017
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A long horizontal capillary tube of uniform bore sealed at one end contains dry air trapped by a drop of mercury. The length of the air column is 142 mm at 17oC. Determine the length of the air column at 25oC.
Date posted:
February 18, 2017
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In verifying the pressure law of gases, the temperature and pressure of a gas are varied at constant volume. State the condition necessary for the law to hold.
Date posted:
February 18, 2017
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State why it is necessary to leave an air space in a closed glass bottle of water when it is to be kept in a refrigerator.
Date posted:
February 18, 2017
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Name two factors that affect the boiling point of a liquid.
Date posted:
February 18, 2017
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Water is known to boil at 100oC. A student heated some water and noticed that it boiled at 101oC. State two possible reasons for this observation.
Date posted:
February 18, 2017
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During the electrolysis of aqueous silver nitrate, a current of 5.0 A was passed through the electrolyte for 3 hours.
a) Write the equation for the reaction which took place at the anode
b) Calculate the mass of silver deposited. (Ag = 108; IF = 96500 C)
Date posted:
February 16, 2017
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a) When brine is electrolysed using inert electrodes, chlorine gas is liberated at the anode instead of oxygen. Explain this observation.
b) Name the product formed at the cathode.
Date posted:
February 16, 2017
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During purification of copper by electrolysis, 1.48 g of copper were deposited when current was passed through aqueous copper (II) sulphate for 2$\frac{1}{2}$ hours. Calculate the amount of current used. (Cu = 63.5; 1 F = 96500 C).
Date posted:
February 16, 2017
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An element P has a relative atomic mass of 88. When a current of 0.5 amperes was passed through the fused chloride of P for 32 minutes and 10 seconds, 0.44 g of P were deposited at the cathode. Determine the charge on an ion of P.
(1 Faraday = 96500 Coulombs)
Date posted:
February 16, 2017
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Give reason why aluminium metal would protect iron from rusting better than zinc metal.
Date posted:
February 16, 2017
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Aqueous potassium sulphate was electrolyzed using platinum electrodes in a cell.
a) Name the products formed at the cathode and anode
b) How does the concentration of the electrolyte change during electrolysis?
c) Why would it not be advisable to electrolyse aqueous potassium sulphate using potassium metal electrodes?
Date posted:
February 16, 2017
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Explain why a drop of methylated spirit on the back of the hand feels colder than a drop of water at the same temperature.
Date posted:
February 15, 2017
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Water of mass 3 kg, at a temperature of 90oC is allowed to cool for 10 minutes. State two factors, other than humidity, that determine the final temperature.
Date posted:
February 15, 2017
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A heating coil is rated 100 W, 240 V. At what rate would it dissipate energy it is connected to a 220 V supply
Date posted:
February 15, 2017
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An electric bulb with a filament of resistance 480 ohms is connected to a 240 V mains supply. Determine the energy dissipated in 2 minutes
Date posted:
February 15, 2017
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An electric heater rated 240 V, 3000 W is to be connected to a 240 V mains supply, through a 10 A fuse. Determine whether the fuse is suitable or not
Date posted:
February 15, 2017
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State three factors that affect the capacitance of a parallel plate capacitor
Date posted:
February 15, 2017
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State and explain how the rate of reaction between zinc granules and steam can be increased.
Date posted:
February 15, 2017
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State the Hess's Law and its applications.
Hess's law States that if a chemical change can be made to take place in two or more steps, the amount of the total heat change is the same no matter which method is used.
Its applications are:
1.Determination of heat of formation of substances which cannot be measured experimentally. Substances like methane,carbon dioxide and benzene cannot be prepared by uniting there elements. Therefore it is not possible to measure the heat of formation of certain compound directly.
2.Determination of heat of transition. The heat of transition from one allotropic form to another can also be calculated with the help of Hess's law.
3.Determination of heat of various reaction. By using Hess's law we can calculate enthalpies of many reactions which can not be measured directly. For example the enthalpy of dimerization of nitrogen dioxide.
Date posted:
February 15, 2017
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State two factors that should be considered when choosing fuel for cooking.
Date posted:
February 15, 2017