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Ans. (a) The eating up of metals by the action of air, moisture or a chemical (such as an acid) on their surface is called corrosion.
Prevention of corrosion:
(i) Corrosion or rusting of iron can be prevented by painting, oiling, greasing, galvanising, crome plating, anodising.
(ii) Corrosion of metals can also be prevented by alloying them with suitable metals or non metals in a required proportion.

(b) M is in the middle of the reactivity series. Various steps which can be used to extract it from its enriched sulphide ore are as follows:
(i) Roasting: The enriched sulphide ore of ‘M’ is strongly heated in the presence of air to convert it into metal oxide.
(ii) Reduction: The metal oxides obtained by roasting is converted to free metal ‘M’ by reducing agents like carbon, aluminium, sodium or calcium.
(iii) Refining: The metal ‘M’ obtained by reduction contains some impurities. Thus this impure metal ‘M’ undergoes purification. The process of purifying impure metal is called refining. The most widely used method for refining is electrolytic refining.

Q.16. (a) State Fleming’s left-hand rule. Apply this rule and find the direction of force acting on the electron that enters a magnetic field at right angles to it as shown in the figure.
(b) When is an electric circuit said to be overloaded? State two measures to avoid it. What name is given to a situation in which the live and the neutral wires accidentally come in contact? State the role a safety device may play in this situation.

Ans. (a) According to Fleming’s Left Hand Rule: Hold the forefinger, the centre finger and the thumb of your left hand at right angles to one another. Adjust your hand in such a way that the forefinger points in
the direction of magnetic field and the centre finger points in the direction of current, then  the direction in which thumb points, gives the direction of force acting on the conductor.

• In the given example the direction of force acting on the electron is out of the page because the direction of force is perpendicular to the direction of magnetic field and current given by Fleming’s Left Hand Rule. The direction of current is taken opposite to the direction of motion of electrons i.e. in this case in the downward (south) direction and direction of magnetic field is towards east. Therefore the force is directed out of the page.

(b) Overloading and measures to avoid it: See Q.2 (L.A.T.), Chapter 13. [Page 149
• When the live and the neutral wires accidentally come in contact, this situation is known as short-circuiting.
• A fuse is the most important safety device. A fuse is a safety device having short length of a thin, tin-plated copper wire having low melting point, which melts and breaks if the current exceeds a safe value. A fuse is used for protecting the circuits and electric appliances from damage at the time of overloading or shortcircuiting of the circuits.

Or

(a) With the help of a diagram describe in brief an activity to show that a magnetic field is produced by a current carrying circular coil. Draw a diagram to show the pattern of the magnetic field lines in this case.

(b) State the function of the earth wire in domestic electric circuits. Why is the metallic body of an electric appliance connected to the earth wire? Write the colour used for insulation of the earth wire.

Science 2009 Question Papers Class X
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