Class 8 Current
Electricity and Magnetism exercise question answer general science
Class 8
general science chapter 4 question answer Class 8
question answer Current Electricity and Magnetism Current Electricity and
Magnetism class 8 question answer maharshtra board
Q.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 ……………….
Ans: 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 …………potential to the point of……………….. potential.
Ans: 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 the negative end of an electric cell is the…………….of the cell.
Ans: The difference between the electrostatic potential of the positive end the negative end of an electric cell is the potentil difference of the cell.
d. Three electric cells of potential difference 1.5 V each have been connected as a battery. The potential difference of the battery will be ……………………V.
Ans:
Three electric cells of potential difference 1.5 V each
have been connected as a battery. The potential difference of the battery will
be 4.5V.
e. An electric current flowing in a wire creates ……………around the wire.
Ans: An electric current flowing in a wire creates magnetism around the wire.
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Q.2. A
battery is to be formed by joining 3 dry cells them with connecting
wires. Show how will you connect the wires by drawing a diagram.
Ans:
Q.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?
Ans:
If you can see the filament of the bulb, check whether it is intact or broken. Check whether the cells are connected in a proper manner :
or in rong way:
if they
are connected in wrong way as shown above, the total potential difference will
be 2V + (-2V)=
zero.
Q.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?
Ans:
6V
8V
Q.5. Describe
the construction, working and usefulness of a dry Cell, with the help of a
diagram.
Ans:
Inside the outer coating find whitish, metal layer. This layer is made up of zinc (Zn) metal layer. This is the negative terminal of the cell. There is another layer inside an electrolyte is filled between these two layers. The electrolyte contains negatively charged and positively charges ions. These are the carriers of electricity. The electrolyte is a wet pulp of zinc chloride (ZnCl2) and ammonium chloride. (NH4Cl). There is a graphite rod at the centre of the cell. This is positive terminal of the cell. A paste of manganese dioxide (MnO2) is filled outside the rod, because of the chemical reaction of all these chemicals, electrical charge is produced on the two terminal and an electric current flows in the circuit.
Due to
the wet pulp used in this cell, the chemical reaction proceeds very slowly.
Hence a large electric current cannot be obtained from this. Compared to the
electric cells using liquids, the shelf life of dry cell is longer. Dry cells
are very convenient to use as these can be held in any direction with respect
to ground and can be used in mobile instruments such as radio sets, wall clocks
and torches.
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Q.6. Describe
the construction and working of an electric bell with the help of a diagram.
Ans:
The above diagram shows the construction of an electric bell and also circuit. The bell consists of an electromagnet, contact screw, iron strip, metal striker and metal gong. A coil of copper wire wound around an iron piece works as an electromagnet and an iron strip along with a striker is fitted near it. A contact screw touches the strip.
The circuit is closed with the key . The current flows in the circuit when the screw is in contact with the iron strip. The current. carrying coil becomes a magnet and attracts the iron strip towards it . As a result, the metal striker hits the metal gong producing sound. At the same time, the screw loses the contact with the strip. The circuit is now incomplete. Hence, no current flows in the circuit. Therefore, the electromagnet loses its magnetism and the electric iron strip returns to its initial condition , making contact with the screw . As the circuit is now completed, the electromagnet attracts the iron strip and the striker strikes the gong producing sound . The action repeats itself and the bell continues to ring till the circuit is broken by opening the key in the circuit.
The
working of the electric bell is thus based on the magnetic effect of electric
current.
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