JK Academy Maharashtra Board Class 8 Science Solutions Chapter 4 Current Electricity and Magnetism
Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 4 Current Electricity and Magnetism Questions and Answers.
Maharashtra State Board Class 8 Science Solutions Chapter 4 Current Electricity and Magnetism
Class 8 Science Chapter 4 Current Electricity and Magnetism Textbook Questions and Answers
Exercise
1. Write proper words from the following group of words in the blanks.
(magnetism, 4.5V, 3.0V, gravitational attraction, potential difference, potential, higher, lower, 0V)
a. Water in the waterfall flows from a higher level to the lower level because of gravitational attraction.
b. In an electric circuit, electrons flow from a point of lower potential to the point of higher potential.
c. The difference between the electrostatic potential of the positive end and the negative end of an electric cell is the potential difference of the cell.
d. Three electric cells of potential difference is 1.5 V each have been connected as a battery. The potential difference of the battery will be 4.5 V.
e. An electric current flowing in a wire creates magnetism around the wire.
2. A battery is to be formed by joining 3 dry cells with connecting wires. Show how you will connect the wires by drawing a diagram.
Answer:
3. In an electric circuit, a battery and a bulb have been connected and the battery consists of two cells of equal potential difference. If the bulb is not glowing, then which tests will you perform in order to find out the reason for the bulb not glowing?
Answer: In order to find out the reason for the bulb not glowing we should perform the following tests:
(i) We need to check how the battery terminals are connected to each other. The positive terminal of a battery is connected to the negative terminal of another battery. Even then if the bulb is not glowing, then we need to perform the next tests.
(ii) We need to check if there are any broken wires in the circuit. If there are broken wires then either fix the wires or replace them. And close the circuit. If this too doesn’t work, then move to the next test.
(iii) We need to check how the connecting wires are plugged into the bulb. This will ensure that the bulb is properly connected to the batteries as shown in the diagram below. Even then, if the bulb does not glow, then follow the next step.
(iv) We also need to check if the filament in the bulb is broken. If it is broken then replace the bulb. Even after all these tests, if the bulb is still not glowing then replace the batteries with new ones.
4. Electric cells having 2V potential difference each have been connected in the form of a battery. What will be the total potential difference of the battery in both cases?
In
figure (i), three cells are connected in series.
∴ Total potential difference = 2V
+ 2V + 2V = 6V.
In figure (ii), four cells are connected in series.
∴ Total potential difference = 2V
+ 2V + 2V + 2V
= 8 V]
5. Describe the construction, working and usefulness of a dry Cell, with the help of a diagram.
Answer: Construction of dry cell: A dry cell consists of the following components –
1. Outer metal cover: The outer metal cover is made up of Zinc metal. It is white in appearance and works as a negative terminal of the cell.
2. Electrolyte: There is the electrolyte filled between the two layers inside the Zinc metal. Electrolyte is a wet pulp which is a combination of Ammonium chloride (NH4Cl) and Zinc chloride (ZnCl2). It is the carrier of electric charge as it consists of both positively charged and negatively charged ions.
3. Metal rod: At the centre of the cell, there is a graphite rod which is surrounded by a paste of Manganese dioxide (MnO2). It is considered the positive terminal of the cell.
4. Working of a dry cell: The chemical reactions take place between the zinc container, electrolyte and graphite rod. Due to this reason, electric charge is produced or generated on the two terminals – positive and negative of the cell and electric current gradually flows into the circuit.
5. Usefulness of a dry cell: A dry cell is usually portable and easy to use. The longevity of a dry cell is more than those cells which use liquid electrolyte. Dry cells can also be used in T.V., torch, toys or Air Conditioner remote controls, etc.
6. Describe the construction and working of an electric bell with the help of a diagram.
A copper wire is wound around an iron piece. This coil acts as an electromagnet. An iron strip along with a striker is fitted near to the electromagnet. A contact screw is in touch with the strip. The electric circuit is connected. The current flows in the circuit when screw is in contact with the strip, and hence the coil becomes a magnet and attracts the iron strip towards it. Therefore, the striker hits the gong and the sound is created. However, at the same time, the contact screw loses the contact with the strip and the current in the circuit stops. In this situation, the electromagnet loses its magnetism and the iron strip moves back and comes in contact with the contact screw. The electric current is then immediately restored and again the striker hits the gong by the above process. This action repeats itself and the bell rings.
Project :
Present all the activities that you performed in this chapter in Science exhibition.