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Three students Shweta, Ayesha and Samridhi were performing an experiment to understand the factors on which the resistance of a conductor depends. Each one of them completed electric circuit with the help of a cell, an ammeter, a plug key and wire.
Shweta put nichrome wire of length ‘l’ in the circuit and after plugging the key, noted current in the ammeter.
Ayesha put nichrome wire of same thickness but twice the length i.e. ‘2l’ in the circuit and after plugging the key, noted current in the ammeter.
Samridhi took copper wire of length ‘l’ and same thickness in the circuit and after plugging the key, noted current in the ammeter.
(a) If the ammeter reading is X ampere with nichrome wire of length ‘l’, then what will be the ammeter reading if the length of nichrome wire is doubled with same area of cross-section ?
(b) What happens to the ammeter reading if the area of cross-section of nichrome wire is doubled, keeping the length of wire ‘l’ the same ?
(c) Define ‘resistivity’. Write its SI unit. Compare the resistivity of an alloy with its constituents metals.
Shweta put nichrome wire of length ‘l’ in the circuit and after plugging the key, noted current in the ammeter.
Ayesha put nichrome wire of same thickness but twice the length i.e. ‘2l’ in the circuit and after plugging the key, noted current in the ammeter.
Samridhi took copper wire of length ‘l’ and same thickness in the circuit and after plugging the key, noted current in the ammeter.
(a) If the ammeter reading is X ampere with nichrome wire of length ‘l’, then what will be the ammeter reading if the length of nichrome wire is doubled with same area of cross-section ?
(b) What happens to the ammeter reading if the area of cross-section of nichrome wire is doubled, keeping the length of wire ‘l’ the same ?
(c) Define ‘resistivity’. Write its SI unit. Compare the resistivity of an alloy with its constituents metals.
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(a) Ammeter reading becomes $\frac{X}{2}$ / halved (1 Mark)
(b) Ammeter reading becomes $2X$ / doubled (1 Mark)
(c) • Resistivity is equal to electrical resistance of a conductor of unit length and unit area of cross section. (1 Mark)
• SI unit = $\Omega\text{ m}$ / ohm metre (½ Mark)
• Resistivity of an alloy is higher than its constituent metals. (½ Mark)
OR
(c) (i) It has high melting point. (1 Mark)
(ii) The resistivity of an alloy is generally higher than that of its constituent metals. / Alloys do not oxidise (burn) readily at high temperatures. (1 Mark)
(b) Ammeter reading becomes $2X$ / doubled (1 Mark)
(c) • Resistivity is equal to electrical resistance of a conductor of unit length and unit area of cross section. (1 Mark)
• SI unit = $\Omega\text{ m}$ / ohm metre (½ Mark)
• Resistivity of an alloy is higher than its constituent metals. (½ Mark)
OR
(c) (i) It has high melting point. (1 Mark)
(ii) The resistivity of an alloy is generally higher than that of its constituent metals. / Alloys do not oxidise (burn) readily at high temperatures. (1 Mark)