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Ans. (a) Element A is a non-metal because it has 7 valence electrons so it accepts 1 electron to complete its octet and form a negative ion.
(b) Element B has a larger atomic size than element C because on moving from left to right in a period of the periodic table, the size of the atoms decreases. On moving from left to right in a period, the atomic
number of elements increases which means that the number of protons and electrons in the atoms increases as the extra electrons are added to the same shell. Due to large positive charge on the nucleus, the electrons are pulled in more close to the nucleus and the size of atom decreases.
(c) Element C has a valency of 1 because there are 7 electrons in its outermost shell. So it requires 1 electron to complete its shell and form monovalent negative ion.

Q.15. (a) An electric bulb is rated as 50 W, 220 V. Calculate the energy consumed by the bulb in 20 minutes. Express your answer in commercial units of electric energy.
(b) Distinguish between overloading and short circuiting in a domestic circuit.
(c) Why is it essential to earth electrical appliances having metallic body?

Sol. (a) Power of the electric bulb = 50 W =kw
Time = 20 minutes =

Energy consumed = Power x time

=

(b) Overloading and short circuiting: See Q.2. (L.A.T.), Chapter 13

(c) Earth wire carries a part of electric current to the earth so as to save the electrical appliances from damage. We earth the metallic body of an electric appliance to save ourselves from electric shocks. If accidently the live wire touches the metal-case of the electric appliance that has been earthed, the current flows directly into the earth and we are saved from the electric shock.

Or

(a) Name the electrical device which converts electrical energy into mechanical energy. State the principle involved in this device.
(b) In the given circuit, calculate :

(i) the total resistance of the circuit,
(ii) current flowing through the circuit,
(iii) potential difference across the lamp and the resistor.

Science 2008 Question Papers Class X
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