Physics (Part-viii) (Railway)

Total resistance of the circuit when resistors are connected in parallel is given by 1/R = 1/R₁ + 1/R₂ +.......

• According to the question, 1/R = 1/10 + 1/20 + 1/30 =11/60

• ∴R = 60/11

• The relation between Power and Resistance is expressed as P = V2 /R where P is the Power measured in watt, R is the resistance measured in ohms, and V is the electric potential measured in volts.

• So, P = 602/60 / 11 = (60* 60 * 11)/60=660 watts

• If M = magnification, f= focal length, and u= object distance, then magnification is given by m = f/(f-u)

• So, according to the question, M= 18/(18-12)= 18/6= 3

The swimming pool appears shallow than it actually is due to the refraction of light.

• It happens because the rays of light coming from the bottom of the swimming pool is refracted by the water and forms a virtual image of the swimming pool bed some height above where the swimming pool bed is.

Magnetic field lines can never cross, meaning that the field is unique at any point in space.

• Magnetic field lines are continuous, forming closed loops without beginning or end. They go from the north pole to the south pole.

For a real and inverted image, the height of the image is negative, and the height of the object is positive. So. the magnification of the mirror is negative.

• If the image is diminished the magnification will be less than one. If the image is enlarged the magnification will be greater than one.

• A concave mirror has negative magnification.

For a spherical mirror, u is distance of object from pole. v is distance of image from pole, and f is focal length of mirror.

• From mirror formula, we get 1/f = 1/u + 1/v

• This relationship can also be expressed as 1/f = u + v / u * v

1/f = 1 / u + 1 / v

Given: f = 12 cm. and v=u+ 10

⇒  1/12 = 1 / u + 1 / u + 10

⇒ u = 20 cm

v = 20 + 10 = 30 cm.

When have magnification, m = v / u = 30/20 = 1.5

I = 1/R  dØ/dt

= - 2/10 = - 0.2 A

The strength of magnetic field produced by a current carrying solenoid depends on:

• The strength of current in the solenoid: Large the current passed through solenoid: stronger will be the magnetic field produced.

• The number of turns in the solenoid; Larger the number of turns in the solenoid, greater will be the magnetic field produced.

• Soft iron used as core material

• The resistivity formula can be represented as follows:

• Resistivity = 1/conductivity

R α I

R α 1/A

R = Pl/A