Physics (Part-viii) (Railway)

R = 2 Ω

I = 5.5 m

P = 110 * 10-⁸ Ωm

A = ?

A = PL/R = 110 * 10-⁸ * 5.5 / 22

= 27.5 * 10-⁸  m²

= 275 * 10-⁷ m²

Given:

1/f = - 15cm, V = - d/3, = d

1/f = 1/V - 1/u

⇒  - 1/15 = - 1/d/3 -  1/-d

⇒ - 1/15 = -3/d + 1/- d

⇒ - 1/15 = - 2/d

⇒ d = 30cm

Magnetic field lines of circular loop carrying current on the axis of the loop is along the axis of the loop itself.

• When a straight current carrying conductor is placed along the axis of the loop, the magnetic field lines are along the loop and have no component perpendicular to the direction of current.

• If we change the direction of the current continuously in the straight conductor, the induced current in the loop will not be constant.

On the moon, since there is no atmosphere, therefore there is no scattering of sun light incident on the moon surface.

• Hence to an observer on the surface of moon (space), no light reaches the eye of the observer except the light directly from the sun.

• Thus, the sky will have no colour and will appear black to an observer on the moon surface.

u = - 2.5f,

v = ?

From mirror formula,

1/v + 1/u = 1/f

1/v + 1/(- 2.5 f) = 1/f

⇒ 1/v + 5 + 2/5 f = 7/5 f

⇒  v = 5 f/7

Now, magnification,

m = - v/u = - (5 f/7)/- 2.5 f = 2/7

The force on a charged particle moving in a magnetic field is at its maximum when the particle is moving at right angles to the direction of the magnetic field and zero when the particle is moving parallel to the field.

• The magnitude of force is at a maximum when the angle between the conductor and the magnetic field is 90 degrees, that is, when the direction of current in the conductor is perpendicular to the magnetic field.

A device that reverses the direction of flow of current through a circuit is called a commutator.

• Commutators are used in dynamos (DC Generators) and many DC Motors as well as universal motors.

• In a motor, the commutator applies electric current to the windings. By reversing the current direction in the rotating windings in each half turn, a steady rotating force (torque) is produced.

• In a generator, the commutator picks up the current generated in the windings, reversing the direction of current with each half turn, converts AC current into DC current.

Small particles scatter light of shorter wavelength and larger particles scatter light of longer wavelength.

• Thus, smaller particles scatter the light of violet and blue colour the most.

• On the other hand, larger particles scatter the light of red and orange colour the most.

R = P(1 / A)

R₁/R₂ = I₁ A₂ / I₂ A₁ = 7 * 5 / 5 * 2

= 35/10 = 7/2

i α I/R

∴ i₁/I₂ = R₂/R₁ = 2/7

The total resistance of a series circuit is equal to the sum of individual resistances. It is expressed as R = R₁ + R₂+ ...

According to the question R = 30 + 6 = 36 Ω