Which of the following acts as a circuit protecting device?

A metal wire is subjected to a constant potential difference. When the temperature of the metal wire increases, the drift velocity of the electron in It ______________.
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For the given mixed combination of resistors calculate total resistance between points A and B.

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A cell of emf 1.1 and internal resistance 0.5 Ω is connected to a wire of resistance 0.5 Ω. Another cell of the same emf is now connected in series with the intention of increasing the current but the current in the wire remains the same. The internal resistance of the second cell is __________.
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P, Q, R and S are four wires of resistances 3, 3, 3 and 4 Ω respectively. They are connected to form the four arms of a wheat-stone bridge circuit. The resistance with which S must be shunted in order that the bridge may be balanced is __________.
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Two resistances of 100 Ω and 200 Ω are connected in series -across a 20 V battery as shown in below. The reading in a 200 Ω voltmeter connected across the 200 Ω resistance is ____________.

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The current through a 4/3 Ω external resistance connected to a parallel combination of two cells of 2 V and 1 V emf and internal resistances of 1 Ω and 2 Ω respectively is _____________.
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A metallic wire of uniform area of cross section has a resistance R, resistivity ρ and power rating P at V volts. The wire is uniformly stretched to reduce the radius to half the original radius. The values of resistance, resistivity and power rating at V volts are now denoted by R', ρ' and P' respectively. The corresponding values are correctly related as ___________.
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The neutral wire in a domestic electric circuit has the colour.

A metal wire is subjected to a constant potential difference. When the temperature of the metal wire increases, the drift velocity of the electron in It ______________.
Fill in the blank with the correct answer from the options given below.