A. 9.123 Χ10^{2}m.

B. 8.235 Χ10^{5}m.

C. 9.467 Χ10^{15}m.

D. 2.276 Χ10^{10}m.

1 light year is the distance traveled by light in vacuum in one year.
1 light year = 3 x 10^{8} x (365 x 24 x 60 x 60) m = 9.46 x 10^{15} m

Yes If a quantity has dimensions then it must have a unit.

It states that the dimensions of each term on both sides of the equation should remain same.

It is defined as (1/12)^{th} of the mass of one _{6}C^{12} atom.

Least count Error

The National physical Laboratory has the responsibility of maintenance and improvement of physical standards, including that of time, frequency etc.

Precision tells us to what resolution or limit the quantity is measured

A. 0.923

B. 0.293

C. 0.329

D. 0.429

We know that

S = D/ where, D is the diameter of the earth
Here, D = 2 6400 km;

A. Taking more number of observation

B. Eliminating the error

C. By taking more care

D. By ignoring the least count (if any) of the instrument

Random errors cannot be eliminated altogether even after taking atmost care. It can only be reduced by taking more number of observations

A. Rydberg constant

B. Wein's constant

C. Solar constant

D. Gas constant

As Wein's constant, b = T, therefore its unit is meter kelvin.

A. frequency

B. velocity

C. time

D. Heat

Frequency = 1 / time

A. +1.6 x 10^{-19} Coulomb

B. -1.6 x10^{18} Coulomb

C. +1.6 x 10^{+18} Coulomb

D. -2.6 x 10^{+19} Coulomb

Proton charge is 1.6 x 10^{-19 }Coulomb^{ }and Electron charge is -1.6 x 10^{-19 }Coulomb

A. meter and second respectively.

B. only second.

C. only meter.

D. only minute.

Since, Light year is a length and Year is time.

A. frequency.

B. velocity.

C. time.

D. heat.

Frequency = 1 / time

A. taking more number of observation.

B. eliminating the error.

C. by taking more care.

D. by ignoring the least count (if any) of the instrument.

Random errors cannot be eliminated altogether even after taking atmost care. It can only be reduced by taking more number of observations.

A. One

B. Two

C. Three

D. Twenty five

A. fermi.

B. micron.

C. debye.

D. light year.

Fermi, micron and light year are the units of length. But debye is the unit of electric dipole moment.

A. 0.9665 cm

B. 0.966 cm

C. 0.967 cm

D. 0.697 cm

A. 1650763.73 periods of the Krypton clock

B. 652189.63 periods of the Krypton clock

C. 1650763.73 periods of the Cesium clock

D. 9192631770 periods of the Cesium clock

One second is the duration of 9192631770 periods of radiation that corresponds to unperturbed transition between the two hyperfine levels of the ground state of Cs-133 atom.

A. Momentum per unit area

B. Momentum per unit area per unit time

C. Momentum per unit volume

D. Density per unit volume

Pressure = force/area = (Momentum / time) / area

A. Work, Energy and Torque

B. Work, Energy and Pressure

C. Work, Density and Torque

D. Force, Energy and Torque

Work = [M^{1}L^{2 }T^{-2}]
Energy = [M^{1}L^{2 }T^{-2}]
Torque = [M^{1}L^{2 }T^{-2}]

A. 2.1 10^{5} Pascal

B. 2.01 10^{2} Pascal

C. 2.01 10^{6} Pascal

D. 1.01 10^{5} Pascal

A. 2.1 10^{30}

B. 2.1 10^{-30}

C. 1.1 10^{30 }

D. 3.1 10^{30}

Number of electrons = total mass / mass of each electron
= 1 kg / 9.11 10^{-31} kg = 1.1 10^{30}

A. 3.6 10^{12} ergs

B. 36 10^{12} ergs

C. 26 10^{12} ergs

D. 36 10^{14} ergs

1 kW h = 10^{3} W h = 10^{3} x 10^{7} erg/s x 60 x 60 s
= 36 x 10^{12} ergs

A. 1.745 10^{-2}

B. 17.45 10^{-2}

C. 1.24 10^{-3}

D. 17.45 10^{-5}

A. 5

B. 6

C. 4

D. 3

For a number less than 1,
1. the zeroes on the right and left to the decimal point are non significant (~~0~~.~~0~~6070).
2. the trailing zeroes and the zeroes occurring between two non-zero digits are significant (0.06__0__7__0__).
3. All the non -zero digits are significant (0.0__6__0__7__0).
Therefore, the number of significant figures in 0.06070 are 4.

A. 3.261 light year

B. 32.6 light year

C. 4.26 light year

D. 3 light year

1 light year = 9.46 x 10^{15} m
1 par sec = 3.1 x 10^{16} m
1 par sec = 3.26 light year

A. P>N>H

B. N>H>P

C. P>H>N

D. N>P>H

Since Proton Length=10^{-15}, Length of nucleus atom=10^{-14}, Length of hydrogen atom=10^{-10}

A. A / B

B. A + B

C. A - B

D. A = B

If two physical quantities have different dimensions then they can not be added or subtracted together. They can be multiplied or divided.

A. 0.001

B. 0.010 × 10^{–1}

C. 0.0001

D. 0.1×10^{–3}

0.99 – 0.989 = 0.001

A. [MLT^{-2}]

B. [M^{-2}LT^{-2}]

C. [M^{-1}L^{2}T^{-2}]

D. [M^{-1}LT^{2}]

Surface Tension = force / length
= MLT^{-2} / L = [MLT^{-2}]

A. 22%

B. 2%

C. 0. 2%

D. 0.02%

A. C^{2}N^{-1}m^{-2}.

B. Nm^{2}C^{-2}.

C. Nm^{2}C^{2}.

D. N^{-1}m^{2}C.

F=(1/4_{0})(q_{1}q_{2}/r^{2}) [Coulomb's law]
When charges(q_{1 }and q_{2}), distance(r) and force(F) are measured in coulomb(C), meter(m) and newton(N) respectively then dimension of
1/4_{0}(Proportionality constant)= (Fr^{2})/(q_{1}q_{2})
= [Nm^{2}C^{-2}]

A. ML^{-1}T^{-2}.

B. M^{-1}L^{3}T^{-2}.

C. M^{-2}L^{-2}T^{-2}.

D. M^{-1}L^{2}T^{-3}.

F=(Gm_{1}m_{2})/r^{2 } (Gravitation Law)

So, G = Fr^{2}/(m_{1}m_{2})
Dimension formulae of force(F), distance(r) and masses(m_{1 }and m_{2}) are MLT^{-2}, L and M respectively.
So, dimension formula of G= (MLT^{-2})L^{2}/M^{2}

A. 10^{18 }m.

B. 10^{12} m.

C. 10^{15} m.

D. 10^{10 }m.

Peta means a quadrillion(10^{15}) times of a unit.

So, 1 peta metre = 10^{15 }m.

A. +1.6 10^{-19} C.

B. -1.6 10^{18 }C.

C. +1.6 10^{+18} C.

D. -2.6 10^{+19} C.

An atom is electrically neutral. It consists of an electron, proton and neutron.
Charge on a neutron is zero.
Charge on an electron is -1.6 10^{-19} C.
So, charge on a proton is equal in magnitude but is opposite in sign to the charge on an electron.

A. Rydberg constant.

B. Wein's constant.

C. gravitation constant.

D. gas constant.

Wein's constant (b) = _{} T
SI unit of wavelength() is metres(m).
SI unit of temperature(T) is kelvin(K).

A. mho.

B. ohm.

C. ohm/m.

D. ohm-m.

Reactance is the effective resistance of an a.c circuit. So, unit of reactance = unit of resistance.

A. 5

B. 6

C. 4

D. 3

When the number is less than 1, the zeros to the left of the non-zero didgt are not significant.

A. centimetres.

B. kilograms.

C. grams.

D. seconds.

Length is measured in centimetre as it is the fundamental unit of length in C.G.S system of units.

A. metre, kilogram, second.

B. mole, kilogram, second.

C. mole, kelvin, second.

D. metre, kilobyte, second.

The full form of M.K.S. is metre,kilogram, second as per the M.K.S systems of units where metre is fundamental unit of length, kilogram is fundamental unit of mass and second is the fundamental unit of time.

A. Nm.

B. N/m.

C. N.

D. m.

S.I unit of work is Nm, as work = force x distance. S.I unit of force is Newton (N)and distance is metre(m).

A. stress.

B. pressure.

C. power.

D. strain.

Strain = change in length /original length or, Strain = change in volume/ original volume. Here, units get cancelled.

A. watt.

B. newton.

C. volt.

D. joule.

POwer is derived quantity. Power = work/time = Joule/second = watt.

A. 1sec

B. 8 sec

C. 5 sec

D. 108 sec

Difference 8 sec

A. Meter Kilogram Second

B. Mole Kilogram Second

C. Mole Kelvin Second

D. Meter Kilobyte Second

A. fermi

B. micron

C. debye

D. light year

Debye is the C.G.S. unit of electric dipole moment.
1 fermi = 1 femtometer = 1 fm = 10^{-15} m
1 micron = 10^{-6} m
1 light year = 9.46 x 10^{15} m

A. [L^{2}T^{-1}] and [LT^{-2}]

B. [L^{3}T^{-1}] and [L^{2}T^{-2}]

C. [L^{-1}T^{1}] and [LT^{-3}]

D. [LT^{-1}] and [LT^{-2}]

v = a + bt
As L.H.S represents velocity, every term on R.H.S must represent velocity.
Thus, a = v = [LT^{-1}] and bt = v or b = v/t = LT^{-1}/T = [LT^{-2}].

A. 1.057 10^{-16} light year

B. 1.057 10^{-26} light year

C. 1.057 10^{-18} light year

D. 2.057 10^{-16} light year

1 light year = 9.46 10^{15} m
Thus, 1 m = 1 / 9.46 10^{15} light year = 1.057 10^{-16} light year.

A. Coulomb^{2}/(Newton-metre)^{2}

B. Coulomb/Newton-metre

C. Newton-meter^{2}/Coulomb^{2}

D. Coulomb^{2}/Newton-meter^{2}

Unit of _{0} is (Coulomb)^{2}/ Newton-metre^{2}.

A. 8.2 10^{20} kg

B. 2.8 10^{30} kg

C. 8.2 10^{30} kg

D. 8.2 10^{10 }kg

1 chander shekhar limit = 1.4 solar mass
= 1.4 2 10^{30 }kg = 2.8 10^{30 }kg.

A. Am^{-1}.

B. Am^{2}.

C. Am.

D. mA^{-2}.

Magnetic dipole moment(M) = IA
SI unit of current(I) = A(ampere).

SI unit of area(A) = m^{2}(square meter)

A. 12x10^{25} m

B. 15x10^{23 }m

C. One year

D. 9.46x10^{15} m

1 light year is the distance traveled by light in one year.
1 light year = (3 x 10^{8}) x (365 x 24 x 60 x 60) m = 9.46 x 10^{15} m

A. [MLT^{–2}]

B. [ML^{–1}T^{2}]

C. [ML^{–1}T^{–2}]

D. [MLT^{2}]

A. [ML^{3}T^{–2}]

B. [L^{3}T^{–1}]

C. [M^{1}L^{3}T^{–2}]

D. [L^{3}T^{–2}]

Rate of flow represents volume flowing per second.

A. 10^{4}

B. 10^{6}

C. 10^{3}

D. 10^{8}

Speed of sound in air = 343 m/s
Distance traveled by sound in 3 s = 343 x 3 s = 1029 m ~ 10^{3} m

A. Coefficient of elasticity: N/m^{2}

B. Surface Tension: N/m

C. Energy: kg m/s

D. Pressure: N/m^{2}

Unit of energy is kg m^{2}/s^{2}.

A. 10^{-3} m

B. 10^{-4} m

C. 10^{5} m

D. 10^{3} m

Size of the nucleus / size of the atom
= x / 10^{7}
= 10^{-14}/ 10^{-10 }= 10^{-4}
x = 10^{-4} 10^{7} m.

A. 10^{30} meter

B. 10^{40} meter

C. 10^{20} meter

D. 10^{33} meter

The diameter of our galaxy is 10^{20} m.

A. Coeff. Of elasticity: N/m^{2}

B. Surface tension: N/m

C. Energy: Kg m/s

D. Pressure: N/m^{2}

Unit of energy is kg m^{2}/s^{2}.

A. Stress

B. Presurre

C. Power

D. Strain

A. Torque

B. Angular momentum

C. Gravitatinaol constant

D. Moment

Angular momentum has same dimensions as Planck’s constant

A. Am^{-1}

B. Am^{2}

C. TmA^{-1}

D. mA^{-2}

Magnetic dipole moment, M = IA
Its unit is given by Am^{2}.

A. Joule

B. m/s

C. m/s^{2}

D. Kgm/s^{2}

From F=m .a

=Unit of mass x unit of Acceleration

=Kgm/s^{2}

A. Meter and Second respectively

B. Only Second

C. Only Meter

D. Only Minute

Since Light year is a length and Year is time

A. 1074.5 Km/h

B. 1174 Km/h

C. 1195.2 Km/h

D. 1274.5 Km/h

km/h = 1000/(6060) m/s then, 332m/s = 332 (18/5)km/h = 1195.2 Km/h

A. 10^{-12}

B. 10^{23}

C. 10^{25}

D. 10^{27}

Mass of earth can be measured by gravitational methods.
M = gR^{2}/ G
R = 6.4 x 10^{6} m, G = 6.67 x 10-11 Nm^{2} kg^{-2} and g = 9.8 m/s^{2}
M = 6.018 x 10^{24} kg ~ 10^{25} kg

According to Avogadro’s theorem, all the atoms in a given specimen of the substance occupy 2/3 rd volume occupied by substance. Consider an atom of mass m and volume V. If M and N are molecular mass of substance and Avogadro’s numbers respectively, the number of atoms of substance having mass.

Assuming that each atom is sphere of radius r, the volume occupied by atoms in substance

Average diameter = D = (2.04 + 2.06 +2.06 + 2.08 + 2.07 + 2.05)/6

or, D = 2.06

Absolute errors in measurements

D_{1} = 2.06 – 2.04 = 0.02 mm

D_{2} = 2.06 – 2.06 = 0

D_{3} = 2.06 – 2.06 = 0

D_{4} = 2.06 – 2.08 = - 0.02 mm

D_{5} = 2.06 – 2.07 = - 0.01 mm

D_{6} = 2.06 – 2.05 = 0.01 mm

Mean absolute error,

Therefore formula is dimensionally correct.

According to question, Fm^{a}v^{b}r^{c}

F= km^{a}v^{b}r^{c}

Writing the dimensions of both the sides, we have

[MLT^{-2}]= [M]^{a}[LT^{-1}]^{b}[L]^{c}

[MLT^{-2}]= [M^{a}L^{b+c}T^{-b}]

comparing the powers ,we have

a = 1

b + c = 1

-b = -2 b = 2

2 + c = 1

c = -1

hence, F = kmv^{2}r^{-1
}F = kmv^{2}/r

the value of k found to be 1 hence

F = mv^{2}/r

Assertion: The displacement of the particles along x-axis is given by the equation x = 6 - 8t + t

Reason: In the time interval 0 < t < 2 acceleration is negative.

A. Assertion is true but reason is false.

B. Assertion and reason both are false.

C. Both assertion and reason are true and the reason is the correct explanation of the assertion.

D. Both assertion and reason are true but reason is not the correct explanation of the assertion.

The velocity of the particle, \text{v}\text{\hspace{0.17em}}\text{=}\text{\hspace{0.17em}}\frac{\text{dx}}{\text{dt}}\text{=}\frac{\text{d}\left(\text{6}\text{\hspace{0.17em}}\text{-}\text{\hspace{0.17em}}\text{8t}\text{\hspace{0.17em}}\text{+}\text{\hspace{0.17em}}{\text{t}}^{\text{3}}\right)}{\text{dt}}={\text{-8 + 3t}}^{2}\text{\hspace{0.17em}\hspace{0.17em} \hspace{0.17em}}\text{Equation-1} The velocity of the particle at different instant of time with in time range. 0 < t < 2 is, \text{v(0)=}\text{\hspace{0.17em}}\text{-8}\text{\hspace{0.17em}}{\text{ms}}^{\text{-1}}\text{, v(1)= -}\text{\hspace{0.17em}}\text{6}\text{\hspace{0.17em}}{\text{ms}}^{\text{-1}}\text{and v(2)=}\text{\hspace{0.17em}}\text{0}\text{\hspace{0.17em}}{\text{ms}}^{\text{-1}} Thus, between time range 0 < t < 2 velocity is negative. Now, let us find the acceleration \text{}\text{}\text{}\text{}\text{}\frac{\text{}}{\text{}}\text{}\frac{\text{}\text{}\text{}\text{}\text{}\mathrm{}{\text{}}^{\text{}}}{\text{}}\text{}\text{}\mathrm{}\text{}\text{}\text{}\text{}\begin{array}{l}\text{a}\text{\hspace{0.17em}}\text{=}\text{\hspace{0.17em}}\frac{\text{dv}}{\text{dt}}\text{=}\frac{\text{d}\left(\text{-8}\text{\hspace{0.17em}}\text{+}\text{\hspace{0.17em}}3{\text{t}}^{\text{2}}\right)}{\text{dt}}\text{\hspace{0.17em}}\text{=}\text{\hspace{0.17em}}6\text{t}\text{}\text{}\text{Equation-2}\\ \text{From equation}-\text{2 it is clear that acceleration is positive and increasing with time}.\\ \text{The sign acceleration is opposite to the sign of velocity it means the particle is speed of the particle is decreasing}.\end{array}

Assertion: The displacement-time graph for the object’s motion with negative acceleration is curved downward.

Reason: The displacement of the object is proportional to the square of the time interval.

A. Assertion is true but reason is false.

B. Assertion and reason both are false.

C. Both assertion and reason are true and the reason is the correct explanation of the assertion.

D. Both assertion and reason are true but reason is not the correct explanation of the assertion.

The displacement of the object moving in a straight line with negative acceleration can be represented by using second equation of motion. \text{s}\text{\hspace{0.17em}}\text{=}\text{\hspace{0.17em}}\text{ut}\text{\hspace{0.17em}}-\text{\hspace{0.17em}}\frac{\text{1}}{\text{2}}{\text{at}}^{\text{2}} According to this equation, if initial speed of the ball is zero then displacement of the object is proportion to the square of the time interval, which is the equation of parabola. The shape of the curve also depends on the sign of acceleration. For positive acceleration, the curve is upward whereas for negative acceleration, the curve is down ward.

Assertion: The equation of motion can be applicable only if acceleration is constant and it is in the same or opposite direction to velocity.

Reason: During uniform motion, the acceleration of the object remains constant.

A. Assertion is true but reason is false.

B. Assertion and reason both are false.

C. Both assertion and reason are true and the reason is the correct explanation of the assertion.

D. Both assertion and reason are true but reason is not the correct explanation of the assertion.

Equation of motion can be applied if the acceleration is in the same or opposite direction to that of velocity as well as when it is zero. The uniform motion means the object covers equal distance in equal interval of time so its acceleration is zero.

Assertion: The stopping distance of a fast moving car is more on a wet road than on a dry road.

Reason: The acceleration of the car is more on the wet surface than on a dry surface

A. Assertion is true but reason is false.

B. Assertion and reason both are false.

C. Both assertion and reason are true and the reason is the correct explanation of the assertion.

D. Both assertion and reason are true but reason is not the correct explanation of the assertion.

The stopping distance and stopping time of a car depends on the road conditions and driver’s reaction time. For a fixed initial speed, the distance covered by the car is inversely proportional to acceleration of the car. It takes longer to stop a car on wet road than dry.

Assertion: The velocity of a body approaching towards us is more than the velocity of a body moving away from us.

Reason: When the object is moving on the same track, the relative velocity between both bodies is equal to the difference of the individual velocities of both bodies in respective direction.

A. Assertion is true but reason is false.

B. Assertion and reason both are false.

C. Both assertion and reason are true and the reason is the correct explanation of the assertion.

D. Both assertion and reason are true but reason is not the correct explanation of the assertion.

When two bodies are moving in opposite directions, relative velocity between them is equal to sum of the velocity of bodies. But, if the bodies are moving in same direction, their relative velocity is equal to difference in velocity of the bodies.

Assertion: Crowded areas have reduced vehicle speed limits.

Reason: According to third equation of motion, the final velocity of the object depends on acceleration and the distance over which it acts.

A. Assertion is true but reason is false.

B. Assertion and reason both are false.

C. Both assertion and reason are true and the reason is the correct explanation of the assertion.

D. Both assertion and reason are true but reason is not the correct explanation of the assertion.

According to third equation of motion, for fixed value of acceleration, a car that is going twice as fast doesn’t simply stop in twice the distance after applying breaks. Let initial velocity of the car is v and it is moving with acceleration a and stopsafter time interval t. If the body is covering a distance x then from third equation of kinematics,x\text{\hspace{0.17em}}=\text{\hspace{0.17em}}-\text{\hspace{0.17em}}\frac{{v}^{2}}{2a} The stopping distance is equal to the square of the initial velocity. Thus, doubling the initial velocity increases the stopping distance by four times.

Assertion: An object slowing down can have positive acceleration.

Reason: The increase and decrease in speed depends upon the direction of motion of an object.

A. Assertion is true but reason is false.

B. Assertion and reason both are false.

C. Both assertion and reason are true and the reason is the correct explanation of the assertion.

D. Both assertion and reason are true but reason is not the correct explanation of the assertion.

In one dimensional motion, the speed of the object decreases when velocity and acceleration have opposite directions. Positive acceleration means that the change in the velocity always remains in the positive direction. Change in speed is independent of direction of motion of the object. The velocity could be in the positive direction when object slowing down or, the velocity could be in the negative direction when the object speeds up.

Assertion: In the given speed-time graph, speed of the object is negative between time interval 0 h to 3h.

Reason: The object is moving in negative direction and its speed decreases with time.

A. Assertion is true but reason is false.

B. Assertion and reason both are false.

C. Both assertion and reason are true and the reason is the correct explanation of the assertion.

D. Both assertion and reason are true but reason is not the correct explanation of the assertion.

The graph and the slopes are in the positive x-y region throughout the time span considered. The body is decelerating in 0 h to 3 h and after that, body is accelerating till 5 h.

Assertion: A ball is thrown upward and returns to the ground. The displacement of ball is always less than the distance covered by the ball during the whole journey.

Reason: The displacement of the ball moving downward or upwards cannot be equal to the distance.

A. Assertion is true but reason is false.

B. Assertion and reason both are false.

C. Both assertion and reason are true and the reason is the correct explanation of the assertion.

D. Both assertion and reason are true but reason is not the correct explanation of the assertion.

Distance is the actual length of the path covered by the ball and it always keeps on increasing from going upward to coming downwards. However, displacement is equal to the distance between point of projection and the maximum height attained by the ball. As the ball moves downward from the maximum height, ball’s displacement keeps on decreasing and shall become zero once it reaches the point of projection.

Assertion: Uniform motion is a kind of motion in which a body covers equal distances in equal intervals of time.

Reason:Uniform motion is always rectilinear motion.

A. Assertion is true but reason is false.

B. Assertion and reason both are false.

C. Both assertion and reason are true and the reason is the correct explanation of the assertion.

D. Both assertion and reason are true but reason is not the correct explanation of the assertion.

In rectilinear motion body moves in a straight-line path so the body may have uniform motion if it covers equal distance in equal intervals of time during its motion. However, a body moving with uniform motion can travel in any direction. For example, the second hand of a clock moves with uniform speed does not have a rectilinear motion.

A. speedometer.

B. audiometer.

C. odometer.

D. tachometer.

The dashboard of an automobile has an instrument called speedometer, which measures how fast the automobile moves. It is usually calibrated in miles per hour or in kilometre per hour.

A. 20 m

B. 25 m

C. 50 m

D. 98 m

A. 72 m.

B. 49 m.

C. 44.1 m.

D. 32 m.

A. zero initial velocity and uniform acceleration.

B. uniform speed.

C. uniform velocity.

D. variable speed.

For uniform velocity or speed s = v t, the graph is a straight line.

For zero initial velocity and uniform acceleration, the equation of motion is .

A. 30°

B. 45°

C. 60°

D. 90°

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

For two balls in air if one is just thrown and other is at the highest point. Then, the time interval between them is t=2 seconds

Now v=u-g t

0=u- g x 2 so, u=19.6 m/s

Hence, for more than two balls in air, the speed must be greater than 19.6 m/s

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 290** Do AU and A^{0} stand for the same unit? Explain.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

Cesium clock (atomic clock)

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 291** What do you mean by measurement of a physical quantity?

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

Angstrom is the unit for lengthwhich is equal to 10^{-10} m. it is normally used to denote very small length like wavelength and astronomical unit is also the unit of length. 1 AU =1.46 X 10^{11 }m and used to denote very large distances like the distances between stars and other celestial bodies.

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 292** What do you mean by unit? Give the characteristics of unit.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

Measurement means comparison of physical quantity with its unit to find out how many times unit is contained in the physical quantity. Like length of room is 17 m .It means that 1 metre is contained 17 times in the length of room.

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 293** Why other methods to measure the time is replaced by cesium atom clock.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

The standard which is taken as reference to compare the physical quantity is called unit. The characterstics of unit are:

1: It should be well defined.

2: It should be easily accessible.

3: It should be easily reproducible at all places.

4: It should not change with time, place and other physical conditions.

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 294** What do you understand by fundamental quantities and units?

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

The is because in cesium atom clock, the measurement of time is 200 times accurate in comparison to other methods of measurement.

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 295** What are the advantages of SI system of units?

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

The quantities which are independent of each other are said to be fundamental quantities. These are length, mass and time. The units of these quantities are called fundamental units. We have some other fundamental quantities temperature, luminous intensity, current, and amount of substance. The unit of these quantities is Kelvin, candela, ampere and mole respectively.

Besides these, two supplementary units are also defined. It is radian for plane angle and steradian for solid angle.

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 296** Metre is well defined in terms of wavelength and time in terms of periods of radiation why?

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

Advantages of SI systems are,

1: It is coherent system of units.

2: This system of units is internationally accepted.

3: This system of unit is very close to cgs system of unit and can easily be changed to that system

4: In this system all multiples and submultiples can be expressed as power of 10.

5: the total number of units is small.

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 297** How the distance of nearest star can be determined?

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

Metre is defined in terms of wavelength because wavelength is accurately defined. It is reproducible in any laboratory. It is not affected by any physical condition. Second is defined in terms of periods of radiation because period of radiation is more accurate than other measurement. Period of oscillation is unaffected by time, place and temperature.

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 298** Explain the method to determine the size of moon

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

The distance of nearest star can be determined by parallax method suppose S_{1} is the nearest star whose distance is to be calculated. Consider some distant star S whose position direction is fixed as earth rotates round the sun. First find the parallax angle _{1} between distant and nearest star when earth is at position P. After 6 months the earth comes on the position Q and given angle becomes _{2}^{. }The total parallax angle subtended by nearby star on the earth’s orbital diameter PQ will be the sum of two angles.

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 299** Explain echo method to find the distance of moon.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

The size of moon can be determined by parallax method. Suppose the diameter of moon is D, which is to be measured. Fix the telescope from a point E on the earth on both the sides of moon to get the value of angle O.The angle is called angular diameter of moon. If d is the distance of moon from earth then by using the formula O =D/d. D can be determined.

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

**Q. 300** Explain SONAR method to find the distance of submarines in sea.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

A LASER beam is the source of intense, monochromatic and unidirectional beam. By sending the laser beam towards moon the distance of moon from earth can be determined. If C is the velocity of laser beam and T is the total time taken by laser beam to go towards moon and to come back then by using the formula S=C*T/2 distance of moon from earth can be calculated. The factor of 2 is coming because time noted for double distance.

A. 19.6 m/s.

B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

**Right Answer is: **

#### SOLUTION

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B. any speed less than 19.6 m/s.

C. more than 19.6 m/s.

D. 9.8 m/s.

SONAR means sound navigation and ranging. It works on the principle of reflection of waves called ECHO.A strong ultrasonic signal is sent towards the bottom of sea. The signal is reflected back from bottom of sea or by hitting some obstacle in the path. These waves are then received by the receiver in the ship. The total time for whole of the operation is known and velocity of ultrasonic waves is known then by using the formula S = V( T/2 ) distance of obstacle or depth of sea can be calculated.

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