Physics (Part-ix) (Railway)

u = 30 cm, m = 1.33

⇒  m= -V/U ⇒ 1.33 = - V/- 30

⇒ V=39.9 cm ∼ 40 cm

Now, (अब) 1/f = 1/V + 1/U

1/f = 1/40 + 1/30 = 1/f = 3 + 4/120

1/f = 7/120

f = 120/7 = 17.14

For series connection, the resultant resistance = R1 + R2 = 6Ω +4Ω=10Ω

• According to Ohm's law, the current, I, flowing through a circuit is directly proportional to the voltage, V, and inversely proportional to the resistance, R

• It is expressed as I = V/R

• ∴ I= 12/10= 1.2 Ampere

If power is delivered at a constant rate, then then the energy can be found by

• E=P x T

• So, according to the question, energy = 40 x 100

= 4000 Joules

The twinkling of stars is due to atmospheric refraction of star-light.

• The atmosphere is made of several layers of different densities and the refractive indices keep on changing continuously.

• As a result, the path of light rays from the star keeps on changing their path continuously.

• So, the number of rays entering, the pupil of eye goes on changing with time and the stars appear twinkling.

The magnetic forces around the area of a magnet is known as a magnetic field.

• By convention, these field lines seem to originate from the north pole and end into the south pole of a bar magnet.

• The direction inverses inside the magnet i.e.. they appear to move from the south pole towards the north pole.

Induced EMF does not depend on R but induced current does.

m = 4

∴ Real magnification

= m² = (4)² = 16

Surface area of film image on Screen = 16 * 100 = 1600 cm²

V = IR

V₁ = I₁R₁ = 5 * 6 =30 ....(i)

V₂  = I₂ R₂  = I * 10 = 10I .....(ii)

Comparing (i) & (ii)

101 = 30

⇒ I = 30/10 = 3

∴ I₂  = 3A

When an object is placed at infinity in front of a convex mirror, the image is formed at the focus behind the convex mirror.

• The image formed is virtual and erect, and much smaller than the object (or highly diminished).

A rheostat is a variable resistor which is used in a circuit to change the resistance of the circuit so that the current changes.

• Since current and resistance are inversely proportional, current decreases with an increase in the resistance of the rheostat and vice versa.