long answer questions name the effect of current responsible for the glow of the bulb in an electric circuit of the following that the bulb does not glow in the circuit shown in the figure 14.11 change the circuit shown in figure 14.11 be observed deflection the magnetic compass what does the deflection magnetic compass in the hit why did the bulb not glow in figure 14.11 what would be the effect of increase in the number of turns in the coil bound around the magnetic compass in figure 14.11 b what will be observed if the number of cells is increased in the circuit shown in figure 14.11 b
Answers
Explanation:
An electric current can produce
(a) heating effect only.
(b) chemical effect only.
(c) magnetic effect only.
(d) chemical, heating, and magnetic effects.
Soln:
The answer is (d) chemical, heating, and magnetic effects.
Explanation:
Electric current causes a chemical reaction when it passes through a conducting solution. This is a chemical effect of electric current.
When an electric current passes through the bulb. Its filament gets heated and bulb starts glowing. This is the heating effect of electric current.
When an electric current is passed through a circuit it produces a magnetic field around it. This is the magnetic effect of electric current.
2. Boojho and Paheli performed experiments taking similar bulbs and cells but two different solutions A and B as shown in Fig.14.1.
NCERT Exemplar Class 8 Science chapter 14 Solutions fig 1
They found that the bulb in the setup A glows more brightly as compared to that of the setup B. You would conclude that
(a) higher current is flowing through the circuit in setup A.
(b) higher current is flowing through the circuit in setup B.
(c) equal current is flowing through both the circuits.
(d) the current flowing through the circuits in the two setups cannot be compared in this manner.
Soln:
Answer is (a) higher current is flowing through the circuit in setup A.
Explanation:
Higher current is flowing through the circuit in setup A because solution A is a good conductor of electricity compared to solution B.
3. Boojho’s uncle has set up an electroplating factory near his village. He should dispose of the waste of the factory
(a) in the nearby river.
(b) in the nearby pond.
(c) in the nearby cornfield.
(d) according to the disposal guidelines of the local authority.
Soln:
The answer is (d) according to the disposal guidelines of the local authority.
Explanation:
Waste disposal is a major concern in the electroplating industry as it causes water pollution and releases a hazardous chemical into water bodies. Hence it should be disposed of according to guidelines of the local authority.
4. When an electric current is passed through a conducting solution, there is a change of colour of the solution. This indicates
(a) the chemical effect of current.
(b) the heating effect of current.
(c) the magnetic effect of current.
(d) the lightning effect of current.
Soln:
Answer is (a) the chemical effect of current
Explanation:
Conducting a solution through electric current cause’s chemical reaction. This causes a change in colour and this is the chemical effect of electric current.
5. Which one of the following solutions will not conduct electricity?
(a) lemon juice
(b) vinegar
(c) tap water
(d) vegetable oil
Soln:
The answer is (d) vegetable oil
Explanation:
Vegetable oil does not contain ions hence it cannot conduct electricity.
6. Which of the following metals is used in electroplating to make objects appear shining?
(a) iron
(b) copper
(c) chromium
(d) aluminium
Soln:
Answer is (c) chromium
Explanation:
Chromium metal is used in electroplating to make objects appear shining because chromium has shining property and is scratch resistant.
7.
NCERT Exemplar Class 8 Science chapter 14 Solutions fig 2
Which of the following solutions will not make the bulb in Fig 14.2 glow?
(a) sodium chlorides
(b) copper sulphate
(c) silver nitrate
(d) sugar solution in distilled water
Soln:
The answer is (d) sugar solution in diluted water
Explanation:
The sugar solution is neither acidic nor basic and it cannot ionize to conduct electricity. Similarly, distilled water has no ions in it to conduct electricity. Hence the mixture of sugar solution and distilled water will not conduct electricity.
Very Short Answer Questions
8.Fill in the blanks
(a) The object to be electroplated is taken as ____________ electrode.
(b) One of the most common applications of chemical effect of electric current is ______________.
(c) Small amount of a mineral salt present naturally in water makes it a______________ of electricity.
(d) Electroplating of ______________ is done on objects like water taps and cycle bell to give them a shiny appearance.
Soln:
(a) Cathode
(b) Electroplating
(c) Conductor
(d) Chromium
9. Why is a layer of zinc-coated over iron?
Soln:
Iron readily reacts with atmospheric air to form rust. In order to prevent it from rusting zinc is coated over iron.
10. Will the solution of sugar in distilled water conduct electricity?
Soln:
No, the sugar solution is neither acidic nor basic and it cannot ionize to conduct electricity.
11. Name the effect of current responsible for the glow of the bulb in an electric circuit.
Soln:
Heating effect of electric current.
Short Answer Questions
12. Boojho made the circuit given in Fig. 14.3 and observed that the bulb did not glow. On Paheli’s suggestion, he added one more cell in the circuit. The bulb now glows. Explain.
NCERT Exemplar Class 8 Science chapter 14 Solutions fig 3
Soln:
On adding another cell current flows through bulb sufficiently to