4. Current Electricity
and Magnetism
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………………….
b. In an electric
circuit, electrons flow from a point of …………..
potential to the point of ……………..potential.
c. The difference between the electrostatic potential of
the positive end the negative end of an electric cell is the ………………… 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.
e. An electric
current flowing in a wire creates…………
around the wire.
Ans:
a.
Water in the waterfall flows from a higher level to the lower level because of potential
differences.
b. In an electric circuit, electron
flow a from of point of higher potential
to the point of lower potential.
c. The differences between the electrostatic potential of the positive end the
negative end of an electric cell is the potential of the cell.
d. Three electric cells of potential difference 1.5 V each have been connected
as a battery. The potential differences of the battery will be 1.5 + 1.5
+ 1.5 = 4.5 V.
e. An electric current flowing in a
wire creates magnetic field around the wire.
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:
or
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:
The
following test should be performed to find the reason why bulb is not glowing:
1 >Check how the
terminals of the batteries are connected to each other: Ensure that the positive terminal
of one battery is connected to negative terminal of other battery. If
the batteries are connected in this this way and even then the bulb does not
glow, go for the next test given below.
2> Check for the broken wires
in the circuit: Ensure
that the wires used for connecting the various electrical components are
nor broken in between i.e. ensure that the circuit is closed. Even after
ensuring that the wires are not broken in between, the bulb does not glow, move
to the next test.
3> Check how the connecting wires are connected
to the bulb: Ensure
that the bulb is connected to the batteries using the connecting
wires as shown below. Even now, if the bulb does not glow, replace the
bulb or the batteries with a new one.
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?
i>
ii>
Ans:
i) Total potential
difference = 2 + 2 + 2 = 6 V
(ii) Total potential difference = 2 + 2 + 2 +
2 = 8 V
5. Describe the
construction, working and usefulness of a dry Cell, with the help of a diagram.
Ans: Construction of dry cell
The dry cell consists of following components:
Outer
metal covering: The metal covering is made up of zinc metal and
is whitish in appearance. It acts as a negative terminal of the cell.
Electrolyte: Inside the Zinc metal, there is the electrolyte filled
between two layers. Electrolyte is a wet pulp of Zinc chloride (ZnCl2) and Ammonium chloride (NH4Cl). It is the charge carrier of electricity as it
contains negatively charged and positively charged ions.
Metal
rod: There is a graphite rod at the centre of the
cell. It is surrounded by paste of Manganese dioxide (MnO2). It acts as the positive terminal of the cell.
Working of dry cell: Chemical reactions take place between the
electrolyte, zinc container and graphide rod. Because of this, electric charge
is produced on the two terminals of the cell and electric current flows in the
circuit.
Use
of dry cell: They are handy and portable. The life of dry
cell is longer than cells using liquid electrolyte. Dry cells can be use in
torch, T.V. or A.C remote controls, toys, etc.
6. Describe the construction
and working of an electric bell with the help of a diagram.
Ans:
Construction of an electric bell
Following are the components of electric bell:
1 Electromagnet:
A copper wire is wound around an iron piece which acts a magnet
when current flows through it.
2 Striker
in touch with contact screw through an iron strip
3 A metal gong
4 A key
or a switch
Working of an electric
bell
When the switch is 'ON' and the screw is in
contact with the iron strip, then electric current flows through the copper
wire which gets magnetised because of electromagnetism. This magnetised copper
wire (or the electromagnet) attracts the iron strip towards it, letting the
striker hit the gong and thus sound is produced. As soon as the striker hits
the gong, the screw loses its contact with the iron strip and therefore,
current stops in the circuit. At this point, the electromagnet loses its
magnetism and the iron strip moves back and comes in contact with the contact
screw. The electric current is then restored in the circuit and again the
striker hits the gong by the above process. This action repeats itself and the
bell rings.