A wire of length 1 m has a resistance of $20 \Omega$ at $0^{\circ} \mathrm{C}$. It is uniformly stretched so that its length increases by $21 \%$. Assuming the volume of the wire remains constant, the percentage change in resistance is $n \%$. Alternatively, if the wire is heated [without stretching] through a temperature of $27^{\circ} \mathrm{C}$ and if the temperature coefficient of resistance of the material of wire is $0.004 K^{-1}$, the percentage change in resistance is $m \%$. The values of $m$ and $n$ are:
2.08 and 1.64
10.8 and 46.4
20.8 and 16.4
1.08 and 4.64
An object is placed 25 cm in front of a fully silvered concave mirror of focal length 15 cm . A plane mirror is placed 35 cm behind the concave mirror on the side opposite to the object. The final image after reflection first from the concave mirror and then from the plane mirror is formed at:
37.5 cm in front of the plane mirror
72.5 cm behind the concave mirror
107.5 cm behind the concave mirror
37.5 cm in front of the concave mirror
A bar magnet of length 12 cm is placed such that its north pole points towards the geographic north. Two neutral points which are separated by 16 cm are obtained on the equatorial axis of the bar magnet. What is the pole strength of the bar magnet if the horizontal component of the earth's field is $1.25 \times 10^{-5} \mathrm{~T}$ ?
3.024 Am
1.042 Am
10.24 Am
2.032 Am
Forces A and B act at a point. The sum of their magnitudes is 50 N and the magnitude of their resultant is 20 N . If the resultant is at $90^{\circ}$ with the smaller force, the magnitudes of A and B , in N are
$28 \mathrm{~N}, 20 \mathrm{~N}$
$40 \mathrm{~N}, 8 \mathrm{~N}$
$29 \mathrm{~N}, 21 \mathrm{~N}$
$35 \mathrm{~N}, 13 \mathrm{~N}$
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