Physics (Part-viii) (Railway)

Magnification of a concave lens or a convex mirror is always positive because they always form virtual and erect images.

• It can be negative or positive for a convex lens or a concave mirror.

• The magnification of an image by convex lens is positive only when the object is placed between focal point(F) and optical centre.

Photosynthesis is a process by which green plants and certain other organisms synthesize their own food i.e.. transform sunlight energy into chemical energy with the help of chlorophyll, carbon dioxide and water.

• Chloroplast, found in plant cells, is the site of photosynthesis.

• It contains chlorophylls a and b that absorb visible light energy and convert it to usable chemical energy in photosynthesis.

P = I²R or

P = V²/R

V= IR

R = V/I = 0.3/15 = 0.02 mΩ

AC and DC Generators utilize electromagnetic induction to generate electricity.

• In AC generators we have slip rings whereas in DC generators we have commutators, whereas both can produce any given amount of voltage.

The sky appears blue due to the scattering of light.

• Our atmosphere contains atoms and molecules of different sizes that scatter different wavelength of light.

• Since blue colour is scattered to the maximum extent by dust particles, the sky appears blue.

Given

Resistane, R = 10Ω

current, I = 5 A

Time 5 min = 300s.

H = I²  Rt

= (5)²  * 10 * 300

= 75000

= 7.5 * 10⁴J

Magnification is defined as the ratio of image height to object height.

• So, it has no unit because it is the measure of ratio and ratio has no unit representation.

A time varying magnetic field induces a Voltage that is proportional to the rate of change of the wrrert producing it with a Positive value indicating an increase in emf and a negative value indicling a decrease in emf.

1/f = 1/u + 1/v = 1/- 21 + 1/7

= 7 - 21/21 * 7 = 2/21

u = - 14 cm

2/21 = - 1/14 + 1/V

1/V = 2/21 + 1/14

= 28 + 21/21 * 14 = 49/294 = 1/6

V = +6 cm