NCERT solution for class 8 || Science || Chapter 14 -Chemical effects of electric current

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NCERT solution for class 8 || Science || Chapter 14 -Chemical effects of electric current

Chapter 14 -Chemical effects of electric current 

Exercise

Q1. Fill in the blanks 

a) Most liquids that conduct electricity are solutions of acids and bases and salts 

b) The passage of an electric current through a solution causes chemical effects .

c) If you pass current through copper sulphate solution copper gets deposited on the plate connected to the negative terminal of the battery.

d) The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating  

Q2. When the free ends of a tester are dipped in a solution the magnetic needle shows deflection can you explain the reason ? 

Answer- The free end of the tester are dipped in the solution of magnetic needle shows deflection because the magnetic needle indicates the electric current is flowing through the wire it shows that the solution is good conductor of electricity and when the free ends dip in it then the circuit is complete

Q3. Name three liquids which when tested in the manner shown in figure may cause the magnetic needle to deflect .

Answer- The liquid maybe acid bases or salt examples citric acid vinegar ground water

Q4. The bulb does not glow in the setup shown in figure list the possible reason explain your answer?

Answer - Due to following reason bulb may not glow 

  • Bulb may be fused 
  • The battery may be exhausted 
  • Maybe any loose connection in wiring 
  • The liquid solution containing may be distilled water

Q5. A tester is used to check the conduction of electricity through two liquids labelled A and B it is found that the bulb of the tester blows brightly for liquid a while it grows very dimly for liquid B you would conclude .

Answer - Liquid  A is better conductor than liquid B

Q6. Does pure water conduct electricity if not what can we do to make it conducting? 

Answer- Pure water does not conduct electricity because it not contain any salts if we pour some salt like a acid Vinay ka lemon juice  etc. in it to make it conducting

Q7. In case of a fire before the firemen use the water houses they shut off the main electrical supply for the area explain why they do this? 

Answer- A water usually contain the salt and it is the good conductor of electricity so to save  themselves from the electric shock the Fireman firstly shut off the main electric supply for that area

Q8. A child staying in a coastal region test is the drinking water and also the sea water with his tester he finds that the compass needle deflects more in the case of sea water can you explain the reason ? 

Answer- Sea water contain more minerals salt than  the drinking water therefore the child sees more deflection in magnetic needle in case of seawater

Q9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour explain? 

Answer- No it is very risky to the electrician to carry out electrical repairs outdoors during heavy downpour or because a water is a good conductor of electricity and it may  causes to getting electric shock

Q10. Paheli had here that rainwater is as good as distilled water so she collected Some rain water in a clean glass tumbler and tested it using a tester to her surprise she found that the compass needle shows deflection what could be the reason? 

Answer- Rainwater is the the insulator of electricity but when it comes down the atmospheric gases particles and dust particles mixed in mixed with it and it make the water good conducting medium of electricity

Q11. Prepare a list of objects around you that are electroplated? 

Answer- Artificial jewellery atoms are silver and gold plated car and cycle handles are chromium plated metal door and drawer handles and zinc plated cold-drink tanks are tin plated household utensils are zinc plated 

Q12. The process that you saw in activity is used for purification of copper a thin plate of pure copper and a thick rod of A copper are used as electrodes copper from a rod is thought to be transferred to the thin copper plate which electrode should be attached to the positive terminal of the battery and why? 

Answer - Pure copper plate should be connected to negative terminal while A copper plate should be connected to positive terminal of electrode as copper ions are positively charged them a attract to the negative electrode terminals

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