Physics

              51. the term’ hydroponics’ is used to describe

                        (a) sound propagation under water

                        (b) cultivation of plants in water

                        (c)   a disease in which patient develops fear of water

                        (d) study of electronic devices which work under water

               52. Air is

                         (a) always a compound

                         (b) always a mixture

                         (c) A compounds in pollution –free zones

                         (d) a mixture in industrial zones

              53.  Ball bearings as used in bicycles, cars, etc, because

                        (a) the actual area of contact between the wheel and axle is increased

                        (b)  the effective area of contact between the wheel and axle increased

                        (c)  the effective area of contact between the wheel and axle is reduced

                       (d) None of the above statements is correct

              54.   rainbow is produced when sunlight falls on ropes of rain. Which of the following physical phenomena are responsible for this?

                    1. Dispersion

                    2. Refraction

                    3. Internal reflection

Select the correct answer using the codes given below

(a)    1 and 2

(b)   1 and 3

(c)    1 and 3

(d)    All of  these

          55. In dry cell (battery), which of the following are used as electrolytes?

(a)    Ammonium chloride and zinc chloride

(b)   Sodium chloride and calcium chloride

(c)    Magnesium chloride and zinc chloride

(d)   Ammonium chloride and Calcium chloride

          56. Conside the following phenomena

                   1.  Size of the sun at dusk

                   2.  Colour of the Sun at dawn

                    3.   Moon being visible at dawn

                    4.  twinkle of stars in the sky

                    5. Polestar belling visible in the sky

Which of the above are optical illusions?

(a)    1,2 and 3

(b)   3, 4 and 5

(c)    1, 2 and 4

(d)   2, 3  and 5

            57. A team of scientists at Brookhaven national Laboratory including those from India created the heaviest anti-matter (anti-helium nucleus.) What is / are the implication / implications of the creation of anti-matter?

1.       It will make mineral prospecting and oil exploration easier and cheaper.

2.       It will help probe the possibility of the existence of stars and galaxies made of anti-matter.

3.       It will help to understand the evolution of the universe.

Select the correct answer using the codes given below.

(a)    Only 1

(b)   2 and 3

(c)    Only 3

(d)   1, 2 and 3

          58. Electrically charged particles form space travelling at speeds of several hundred km/s can severely harm living beings if they reach the surface of the earth. What prevents them from reaching the surface of the Earth?

(a)    The earth’s magnetic field diverts them towards its poles

(b)   Ozone layer around the Earth reflects them back to outer space

(c)    Moisture  in the upper layers of atmosphere prevents them from reaching the surface of the Earth

(d)   None of the above

           59.  Nearly 30% of the solar radiations return back to the space without contributing anything to the Earth’s surface temperature. This amount of radiation is known as

(a)    Black body

(b)   Tropopause

(c)    Earth’s albedo

(d)   Mesopause

            60.  Consider the following metals

1.       Uranium

2.       Radium

3.       Plutonium

Which of these are used in making nuclear weapons?

(a)    1  and 2

(b)   1, 2 and 3

(c)    2  and 3

(d)   1 and 3

Answer:

Some practical units of length, mass, and time

Length	Mass	Time
Light year   = distance travelled by light in one yar in vaccum. 1ly =9.46 x 10 ¹⁵m 1 astronomical unit (A. U.)   = 1.5 x 10 ¹¹m 1parsec  = 3.26 ly         =3.08x10¹⁶ m 1 nautical mile or seamile             = 6020 ft. 1 micron  = 1μm  = 10⁻⁶ m 1 angstron (A˚) = 10⁻¹⁵ m	1 quintol = 10² kg 1 metric ton = 10³ kg 1 atomic mass unit (amu) or Dalton  = 1.66 x 10⁻²⁷ kg 1 slug  = 14.59 kg 1pound = 0.4537 kg 1 Chandrashar limit    = 1.4  times the mass of sun   = 2.8 x 10³⁰ kg	1 solar day   = 86400 sec. 1 year = 365 ½ solar days 1lunar month = 27.3 solar days, Tropical year = It is the year in which total solar eclipse occurs. Leap year = it is the year in which the month of February is of 29 days.

Prefixes used in metric system

Prefix	symbol	Multiplier	Prefix	Symbol	Multiplier
deci	d	10⁻¹	deca	da	10¹
centi	c	10⁻²	hecto	h	10²
milli	m	10⁻³	kilo	k	10³
micro		10⁻⁶	mega	M	10⁶
nano	n	10⁻⁹	giga	G	10⁹
pico	P	10⁻¹²	Tera	T	10¹²
femto	f	10⁻¹⁵	peta	P	10¹⁵
atto	a	10⁻¹⁸	exa	E	10¹⁸
zepto	z	10⁻²¹	zetta	Z	10²¹
yocto	y	10⁻²⁴	yotta	Y	10²⁴

UNIT

Unit: The chosen standard used for measuring a physical quantity is called unit.

Unit should be:

(i)                  Well defined

(ii)                Easy to reproduce

(iii)               Easy to compare

(iv)              Independent of changes in physical conditions

(v)                Internationally accepted

Units are of two types – (i) Fundamental Unit; (i) Derived Unit

System of units _ Unites depend on choice. Each choice of units leads to a new system (set) of units. The internationally accepted systems are (i) CGS system, (ii) MKS System (iii) FPS system (iv) SI Units.

In SI Units, there are seven fundamental units given in the following

Physical Quantity	Si Unit	Symbol
Length	Metre	m
Mass	Kilogram	kg
Time	Second	s
Electric current	Ampere	A
Temperature	Kelvin	K
Luminuous intensity	Candela	Cd
Amount of substance	mole	mol

Besides these seven fundamental units, two supplementary units are also defined, viz, radian [rad] for plane angle and steradian (sr) for solid angle.