31.

A constant pressure air thermometer gave a reading 47.5 units of volume when immersed in ice-cold water and 67 units in a boiling liquid. The boiling point of the liquid, is

• 125^°C

• 100^°C

• 135^°C

• 112^°C

For an enclosure maintained at 1000 K, the maximum radiation occurs at wavelength λ_m. If the temperature is raised to 2000 K, the peak will shift to

• $\frac{5}{2}{\mathrm{\lambda }}_{\mathrm{m}}$

• $\frac{1}{2}{\mathrm{\lambda }}_{\mathrm{m}}$

• $\frac{7}{2}{\mathrm{\lambda }}_{\mathrm{m}}$

• $\frac{3}{2}{\mathrm{\lambda }}_{\mathrm{m}}$

A source of frequency 240 Hz is moving towards an observer with a velocity of 20 m/s. The observer is now moving towards the source with a velocity of 20 m/s. Apparent frequency heard by observer, if velocity of sound is 340 m/s, is

• 268 Hz

• 270 Hz

• 360 Hz

• 240 Hz

Assertion: Soldiers are asked to break steps while crossing the bridge. 

Reason: The frequency of thick marching may be equal to the natural frequency of bridge and may lead to resonance which can break the bridge.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If assertion is false but reason is true.

Which of the following physical wuantity do not have same dimensions?

• pressure and stress

• tension and surface tension

• strain and angle

• energy and work

At a place earth's magnetic field, 5 × 10⁵ Wb/m² is acting perpendicular to a coil of radius R = 5 cm. If  μ_ο / 4$\mathrm{\pi }$ = 10⁷ , then how much current is induced in circular loop?

• 0.2 A

• 0 A

• 4 A

• 40 A

Dimension of resistivity is

• [ M L² T^-2 A^-1 ]

• [ M L³ T^-3 A^-2 ]

• [ M L³ T^-2 A^-1 ]

• [ M L² T^-2 A^-2 ]

If electron is moving from A to B in wire AB, then current induced in the coil is

• anticlockwise

• clockwise

• arbitrary direction

• no current will be induced

A wire length l carries a steady current. It is bent first to form a circular plane loop of one turn. The magnetic field at the centre of the loop is B. The same length is now bent more sharply give a to double loop of smaller radius. The  magnetic field at the centre caused by the same is

• B

• B/4

• 4B

• B/2

A metal rod consumes power P on passing current. If it is cut into two half and joined in parallel, it will consume power

• P

• 2P

• P/4