Physics (Part-VII) (Railway)

• So, M= 9/(9-18) = 9/-9=-1

• For diverging or convex mirrors, the focal length is always positive.

• For a converging or concave mirror, the focal length is always negative.

• The focal length of a convex mirror is half of its radius of curvature.

• Magnetic field lines never cross each other.

• The magnetic field is the area around a magnet in which the effect of magnetism is felt.

• Therefore, when the direction of motion of the coil is at right angles to the magnetic field, the induced current is the highest.

I α dø/dt

I = A dø/dt

T = -AB sin ω

when ω = 90°, n induced current will be maximum where,

ø  = magnetic flux

I = Induced current

B= magnetic flux density

ω = angle between direction of motion of the coil and magnetic fielt

A = Cross Sectional and area.

• So, f =1/D = 1/3 = 0.33 metres

• According to the equation I = V/R, or R = V/I

• From the question, R = 4.2 Ω and V = 220V

• So, I = 220/4.2 = 52.38 A

• Among the given options, Glass has the highest resistivity of 1010 -1014Ω

• Being an alloy, Nichrome (100 x 10-⁶) has higher resistivity than silver, copper and aluminium.

• Higher wavelengths bend less, whereas shorter wavelength bend more.

• Out of all violet has the least wavelength and hence it bends the most and red has the highest wavelength, so it bends the least.

• It is independent of the shape and size of the materials but depends on the nature and temperature of the materials.

• The resistivity of the material will not change (remain the same) as it is independent of the length or cross-section of the wire.

• In it, all the incident sun rays are converged to the focal point and hence energy radiations are focussed at a single point.

• So, they are used to concentrate light on a given spot.