Class 8 Science - Chapter Chemical Effects of Electric Current NCERT Solutions | A tester is used to check the conduction

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.

The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transfered to the thin copper plate. Which electrode should be attached to the positive terminal of battery and why?

Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.

Does pure water conduct electricity? If not, what can we do to make it conducting?

Prepare a list of objects around you that are electroplated.

The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.

Fill in the blanks
(a) Most liquids that conduct electricity are solutions of , ______________ and ______________.
(b) The passage of an electric current through a solution causes ______________ effects.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the terminal of the battery.
(d) The process of depositing a layer ofany desired metal on another material by means of electricity is called .

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

Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise she found that the compass needle showed deflection. What could be the reasons?

When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

Which of the following can be beaten into thin sheets?
  (a) Zinc     (b) Phosphorus     (c) Sulphur     (d) Oxygen

Give two examples each of situations in which you push or pull to change the state of motion of objects.

Fill in the blanks:
(a) Friction opposes the _____________ between the surfaces in contact with each other.
(b) Friction depends on the _____________ of surfaces.                                                                                                                                                                      (c) Friction produces __________.
(d) Sprinkling of powder on the carrom board ________ friction.
(e) Sliding friction is ___________ than the static friction.

List conditions under which combustion can take place.

Indicate whether the following statements are True (T) or False (F).
(a) Unicellular organisms have one-celled body. (T/F)
(b) Muscle cells are branched. (T/F)
(c) The basic living unit of an organism is an organ. (T/F)
(d) Amoeba has irregular shape. (T/F)

Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth.

Fill in the blanks:
(a) A place where animals are protected in their natural habitat is called                  .
(b) Species found only in a particular area is known as                          .
(c) Migratory birds fly to far away places because of                     changes.

Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room. Explain.

What are the different ways in which water gets contaminated ?

Explain the importance of reproduction in organisms.

Choose the most appropriate answer:
(a) Internal fertilization occurs
      (i) in the female body.
      (ii) outside the female body.
      (iii) in male body.
      (iv) outside male body.

(b) A tadpole develops into an adult frog by the process of
      (i) fertilization   (ii) metamorphosis   (iii) embedding    (iv) budding

(c) The number of nuclei present in a zygote is
      (i) none   (ii) one    (iii) two    (iv) four

Explain how you can take care of your eyes.

Describe characteristics and uses of coke.

Word game : Use the clues to work out the words.

Across
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone
10. Female hormone

Down
1. Male hormone
2. Secretes thyroxine
3. Another term for teenage
5. Hormone reaches here through blood stream
6. Voice box
7. Term for changes at adolescence

Match the organisms in Column I with their action in Column II.
      Column I                           Column II
  (i) Bacteria                       (a) Fixing Nitrogen
  (ii) Rhizobium                  (b) Setting of curd
  (iii) Lactobacillus             (c) Baking of bread
  (iv) Yeast                         (d) Causing Malaria
  (v) A protozoan               (e) Causing Cholera
  (vi) A Virus                      (f) Causing AIDS
                                          (g) Producing antibodies

Choose the correct option.

(a) Adolescents should be careful about what they eat, because
(i) proper diet develops their brains.
(ii) proper diet is needed for the rapid growth taking place in their body.
(iii) adolescents feel hungry all the time.
(iv) taste buds are well developed in teenagers.

(b) Reproductive age in women starts when their
(i) menstruation starts.
(ii) breasts start developing.
(iii) body weight increases.
(iv) height increases.

(c) The right meal for adolescents consists of
(i) chips, noodles, coke.
(ii) chapati, dal, vegetables.
(iii) rice, noodles and burger.
(iv) vegetable cutlets, chips and lemon drink.

Write notes on—
(a) Adam’s apple.
(b) Secondary sexual characters.
(c) Sex determination in the unborn baby.

At an individual level, how can you help reduce air pollution?

Explain how soil gets affected by the continuous plantation of crops in a field.

Fill in the blanks:
(a) A place where animals are protected in their natural habitat is called                  .
(b) Species found only in a particular area is known as                          .
(c) Migratory birds fly to far away places because of                     changes.