18 August 2012

Chemical Effect of Electric Current VIII (8th) Physics Chapter Based Formative Assessment

Physics Chapter-Chemical Effect of Electric Current :Formative Assessment
Q.1: Fill in the blanks: Oral Questions
(i) Most liquids that conduct electricity are solutions of ---------, ---------- and ----------------
Ans: acids, bases, salt
(ii) The passage of an electric current through a solution causes ----------- effect.
Ans: Chemical
(iii) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the -------------- terminal of the battery.
Ans: negative
(iv) The process of depositing a layer of any desired metal on another metallic object, by means of electricity, is called ---------------.
Ans: electroplating.
(v)------- is an instrument to measure across any two points.
Ans: Volt meter
(vi)------------- is rate of the flow of current
Ans: Electric current
(vii) Decomposition of an electrolyte on passing electricity is called -------
Ans: Electrolysis
(viii)Chemical effect of current involve transformation of --------- energy into chemical energy.
Ans: Electrical
(ix) --------- is a source of energy give direct current.
Ans: Cell ( battery –a combination of chemical cells)
(x) --------- in an instrument used to measure flow of current
Ans: Ammeter
Short and very short type Answer Questions
Q.1. At which electrode hydrogen and oxygen gas evolved during electrolysis of water?
Ans: Hydrogen at cathode connected to negative terminal and oxygen to anode connected to positive terminal.
Q.2: When the free ends of a tester are dipped into a solution the magnetic needle shows deflection. Can you explain the reason?
Ans: Electric current flow through the tester and creates magnetic field which causes deflection of the magnetic needle of a compass.
Q.4: Name the two processes based on the principal of electrolysis?
Ans: Refining and Electroplating
Q.6: What can we do to make pure water a good conductor of electricity?
Ans: Pure water does not conduct electricity. We add electrolyte like acid, base or salt to make it conductor.
Q.8: A child staying in a coastal region tests the drinking water and also the sea water with his tester. He finds that his tester needle deflects more in case of sea water. Can you explain the reason?
Ans: Drinking water has less salt impurities than the sea water. therefore his tester needle deflects more in case of sea water.
9. How can you prove conducting properties of substances when the current is very small and bulb does not glow?
Ans: By using magnetic compass.
10. What is LED, why is it the most preferable source of electricity?
Ans: Light Emitting Diode is an electronic device that emits light even when a weak current passes through it and consumption is lesser  than Ordinary  so, is it the most preferable source of electricity .we use it  for many purposes like in traffic signals, on railway platforms as a indicators in different color
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·         8th Combustion and Flame 
·         8th metal and non metal 

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