Effects of Electric Current
Q19. When the free ends of a tester are dipped into a solution,
the magnetic needle shows deflection. Can you explain the reason?
Ans. The deflection in magnetic needle shows that the
circuit is complete and the solution conducts electricity.
Q20. Which metal is usually electroplated on car parts such as
bumpers and bicycle handlebars made of steel?
Ans. Chromium is usually electroplated on car parts
such as bumpers and bicycle handlebars made of steel.
Q21. Which metal is electroplated on iron for making cans and
Ans. Tin is electroplated on iron for making cans
because tin is less reactive than iron. Thus, food does not come into contact
with iron and is protected from getting spoilt.
Q22. Why is the current in the circuit weak?
Ans. Though a material may conduct electricity, it may
not conduct it as easily as a metal. As a result, the circuit of the tester may
be complete and yet the current through it may be too weak to make the bulb
Q23. Why do brand new cycles have shiny handlebars and wheel
rims what will happen if these are scratched?
Ans. A brand new bicycle has shiny handlebar and wheel
rims. However, if these are accidentally scratched, the shiny coating comes off
revealing a not so shiny surface beneath.
Q24. Why is it dangerous to touch a working electrical appliance
with wet hands?
Ans. It is dangerous to touch a working electrical
appliance with wet hands because the tap water is a good conductor of
electricity due to which it may conduct electric current and gives us an
Q25. Write two common application of the chemical effect of
Ans. Two common application of the chemical effect of
electric current are:
Electroplating of metals
Purification of metals
Q26. For electroplating copper on an iron object, which terminal
of the battery (positive or negative) is connected to the iron object?
Ans. In the process of electroplating, the metal to be
electroplated is taken as cathode (negative) and the one used for coating is
chosen as the anode (positive). Thus, negative terminal will be connected to
the iron object.
Q27. In case of a fire, before the firemen use the water hoses,
they shut off the main electrical supply for the area. Explain why they do this.
Ans. Water is a conductor of electricity, so if the
electricity supply is not cut off and firemen come in contact with wet electric
switches, electric wires and other electrical appliances, they may get
Q28. Why the bulb glows when the electric current passes through
Ans. Due to the heating effect of current, the
filament of the bulb gets heated to a high temperature and it starts glowing. However,
if the current through a circuit is too weak, the filament does not get heated
sufficiently and it does not glow.
Q29. What is meant by the chemical effect of electric current? Give
Ans. The passage of an electric current through a conducting
liquid causes chemical reactions. The resulting effects are called chemical
effects of currents. Example – Deposit of metal formed when electric current is
passed through copper sulphate solution (during electroplating).
Q30. Which properties of chromium metal make it suitable for
Ans. The properties of chromium metal that make it
suitable for electroplating are:
It has a shiny appearance.
It does not corrode.
It resists scratches.
Q31. Name three liquids, which when tested in the manner shown
in Figure, may cause the magnetic needle to deflect.
Image from NCERT
Ans. Tap water, vinegar and lemon juice are conductors
of electricity. Most liquids that conduct electricity are solutions of acids,
bases and salts.