TyroCity: Physics XI Notes

Units in different systems

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Generally we can use any convenient unit to measure a physical quantity depending on how much magnitude we are measuring or in which system of units we want to measure it.
What kind of unit we should use?
The unit i) must be accepted internationally.
ii) Should be reproducible.
iii) Should be invariable.
iv) Should be easily available.
v) Should be consistent.
vi) Should be large, if the physical quantity to be measured is a big quantity.
Ex: To measure larger lengths we use units like Km, mt etc, to measure large magnitude of time we use units like hour , day ,week, month , year etc.
vii) Should be small if the physical quantity to be measured is small.
Ex: To measure small time we use units like millisecond, microsecond etc
To measure small lengths we use units like millimeter, centimeter etc.

Types of physical Quantities.:
We can broadly divide the physical quantities in to two types

i)Fundamental Physical quantities
ii)Derived physical quantities.

Fundamental physical quantities: A physical quantity which can exist independently is called Fundamental physical quantity.
Ex: Length, mass and time etc.

Derived physical quantities: A physical quantity which can not exist independently is called derived physical quantity. (Or) A physical quantity which is dependent or derived from any other physical quantity is called derived physical quantity.
Ex : Area, volume, density, speed, acceleration, force, energy etc.
Like the physical quantities we can divide the units in to two types. I)Fundamental units ii)derived units.

Fundamental units : The units of fundamental physical quantities are called fundamental units, (or) The units which are independent or can not derived from any other unit is called fundamental unit.
Ex:Every unit of length is fundamental unit (irrespective of the system to which it belongs);millimeter, centimeter, meter, kilometer etc.
Every unit of time is a fundamental physical quantity ; microsecond, millisecond, second, minute, hour, day etc.

Derived units: The units of derived physical quantities are called derived units. Units of area, volume, speed, density, energy etc are derived units.
Ex: Every unit of speed is a derived unit ; m/sec, cm/sec, km/hr etc.
Every unit of density is a derived unit; kg/m³, gr/cm³ etc.
Every unit of acceleration is a derived unit; m/sec², cm/sec², km/hr² etc.

Systems of units:To measure the fundamental physical quantities Length, Mass and time we have three systems of units, they are i) C.G.S System (Metric system)ii)F.P.S System (British system) and iii)M.K.S System. In all these three systems only three physical quantities length, mass and time are considered to be fundamental quantities.

But, in systems International (S.I) system there are seven fundamental physical quantities. Which are i)Length ii)Mass iii)Time iv)Electric current v)Thermo dynamic temperature vi)Luminous intensity vii)Quantity of substance.
In addition to these two more quantities were added as supplementary physical quantities. They are i)Plane angle ii)Solid angle.

Systems,Fundamental physical quantities and their units:In
C.G.S system: Length (centimeter); Mass (gram); Time (second).
F.P.S system :Length (foot);Mass(pound);Time (second).
M.K.S system: Length (meter); Mass (kilogram); Time (second).
S.I System:Length (meter); Mass (kilogram); Time (second); Electric current (ampere); Thermodynamic temperature (kelvin); Intensity of light (candela); Quantity of matter (mole). The units of suplimentary quantities are Plane angle( radian); Solid angle(Steradian).

Why is a cow more stable than a man?

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

The C.G. of the cow is lowered to the base of the body and the base of the foot is greater than the man, so the cow is more stable than the man.

What is meant by elastic and inelastic collision?

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

The collision in which total linear momentum and total K.E. is conserved is called elastic collision.

i.e. In elastic collision,

m1u1 + m2u2 = m1v1 + m2v2

½(m1u1²+ m2u2²) = ½(m1v1² + m2v2²)

Eg: Collision between atomic or sub-atomic particles, collision between gas molecules, etc.
The collision in the total linear momentum is conserved but the total K.E. is not conserved is called inelastic collision.
i.e. In inelastic collision,

m1u1 + m2u2 = m1v1 + m2v2
But,
½(m1u1² + m2u2²) ≠ ½(m1v1² + m2v2²)

Eg: A bullet embedded in a target is one example of inelastic collision.

Explain why spokes are fitted in the cycle wheel.

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

The spokes of cycle wheel increases its moment of inertia. The greater the moment of inertia, the more is the opposition to any change in uniform rotational motion. As a result cycle runs smoothly and steadily. Of the cycle wheels had no spokes, the cycle would be driven jerky and hence unsafe.

Explain why a man carrying a load on his back leans forward?

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

To be in stable equilibrium, the vertical line through the C.G. should pass through the base of the man. So, a man carrying a load on his back leans forward to the opposite side to make the vertical line through the C.G. pass though the base and hence to be stable.

Can a body be regarded in a state of rest as well as in motion at the same time? Give an example.

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Yes. For example, two passengers in a moving bus are at rest with respect to each other but they are in motion with respect to a person standing at the side of the road.

Differentiate between conservation of kinetic energy and conservation of linear momentum.

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Conservation of kinetic energy	Conservation of linear momentum
Conservation of kinetic energy is possible only in elastic collision.	Conservation of linear momentum is possible in both elastic and inelastic collision.
Collision between the atomic molecules and subatomic particles is elastic collision. K.E. is conserved here.	Collision of bullet with its target is inelastic collision. K.E. is not conserved here.

NEB Model Question for Physics – Class 11

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

HSEB Model Question for Physics – Class 11
CLASS : 11
For : 2070
Time : 3 hrs
Full Marks : 75
Pass marks : 27

Group A

Q.1. Answer in brief, any SIX questions. [2 X 6 = 12]

What is the difference between accurate and precise measurement ?
A ball having a momentum P hits a bat and its momentum becomes â€“P. What is the change in the momentum of the ball ?
State the condition of equilibrium of a system of co planer forces.
Does the acceleration of a body moving in a circular path remain constant?
Sand it thrown on the covered with snow. Why ?
Since the moon is constantly attracted towards the earth by the gravitational interaction, why doesn’t it crash into the earth ?
Explain in term of breaking stress why elephant has thicker legs as compared to human beings ?

Q.2. Answer in brief, any TWO questions . [2 X 2 = 4]

Why are two thin blankets warmer than a single blanket of double the thickness ?
Distinguish between saturated and unsaturated vapor pressure.
Does the coefficient of linear expansion depend on length ? Explain.

Q.3. Answer in brief, any ONE question : [1 X 2 = 2]

Can a convex mirror ever from a real image? If so, explain with diagram.
What are grazing incidence and grazing emergence ?
Q.4. Answer in brief, any ONE question : [2 X 1 = 2]
A man inside an insulated metallic cage does not receive shock when the cage is highly charged. Explain.
Is it possible to charge a capacitor to any potential?

Group B

Q.5. Answer any THREE questions : [4 X 3 = 12]

State the principle of conservation of linear momentum. How does Newton’s third law of motion lead to the principle of conservation of linear momentum ?
Prove that the total mechanical energy in gravitational field is always conserved. Also explain conservation and non-conservative forces.
What is SHM? Show that the motion of a bob of a simple pendulum is simple harmonic. Find its time period.
What is capillarity? Deduce an expression for the rise of a liquid in simple tube.

Q.6. Answer any TWO questions : [4 X 2 = 8]

Define specific latent heat of fusion of a solid. Develop an expression for the latent heat of fusion of ice.
Define the coefficient of thermal conductivity of a substance. Describe Searle’s method for determination of the thermal conductivity of a good conductor.
What is a Carnot engine ? Derive an expression for its efficiency.

Q.7. Answer any ONE question : [ 4 X 1 = 4 ]

Define power of a lens. Derive the formula for the effective power of two thin lenses in contact.
Describe the construction and working of a compound microscope and hence derive an expression for its magnifying power.
Q.8. Answer any ONE question : [4 X 1 = 4]
State Gauss law. Apply it to obtain an expression for electric field outside the charged special conductor.
Find the equivalent capacitance of two capacitor when they are in (i) Series and (ii) parallel.

Group C

Q.9. Solve any Three numerical questions : [4 X 3 = 12]

A ballet dancer spins with 2.4 rev/s with her arms outstretched when the moment of inertia about the axis of rotation is I. With her arms folded, the moment of inertia about the same axis becomes 0.6 I. Calculate the new rate of spin.
A canoe has a velocity of 0.4 m/s south east relative to the earth. The canoe is on a river that is flowing 0.5 m/s east relative the earth. Find the magnitude and direction of the velocity relative to the river.
The sun has a mass 330,000 times that of the earth. For a person on earth, the average to the centre of the sun is 23,500 times the distance to the center of the earth. In magnitude, what is the ratio of the sun’s gravitational forces on you to the earth’s gravitational forces on you ?
Castrol oil at 20oC has coefficient of viscosity 2.42 Nsm-2 and a density 940 Kgm-3. Calculate the terminal of a steel ball of radius 2.0 mm falling under gravity in the oil.

Q.10. Solve any TWO questions : [4 X 2 = 8]

A ball of copper of specific heat capacity 400 Jkg-1K-1 weighting 400 gm is transferred from a furnace to 1 Kg of water at 20oC. The temperature of water rises to 50oC. What is the initial temperature of the ball ?
An ideal gas initially at 4 atmosphere and 350 K is permitted to expand adiabatically to 1.5 times its initial volume. Find the final pressure and temperature to 1.5 times its initial volume. Find the final pressure and temperature if the gas is (i) monatomic and (ii) diatomic with Cv = 5/2 R.
At what temperature will the average speed of oxygen molecules be sufficient so as to escape from the earth? Escape velocity from the earth is 11.2 Km/s and mass of one oxygen molecules is 5.34 X 10-26 Kg.

Q.11. A microscope is focused on the upper surface of a glass plate. A second plate is then placed over the first. In order to focus on the bottom surface of the second plate, the microscope must be raised 1 mm. In order to focus on the upper surface , it must be raised 2 mm farther. Find the index of retardation of the second plate.

Q.12. Two point charges +1 µC are placed at a distance of 0.12 m apart. Determine the point on the line joining two charges where net forces acting on the positive charges is zero.

Photometry- Old is Gold

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

Why does the illuminance of a surface decrease as it moved away from the light source?
What is the meaning of Luminous intensity?
Define luminous flux. State its unit of measurement.
What are the factors on which the illuminance of a surface depends?
Define luminous efficiency of a source of light and give its SI unit.
What is the difference between lumen and lux?
Define illuminance. Name the factor upon which it depends.
The sun is less bright in morning and in evening as compared to that at noon although its distance from the observer is almost the same. Why?
Distinguish between illuminance and luminance.

What do you mean by geo-stationary satellite? Explain?

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

The satellite which appears to be at rest from the surface of the earth is called geo-stationary satellite. The time period of geo-stationary satellite is equal to the time period of the earth. The orbit of geo-stationary satellite is called parking orbit.

Lenses – Old is Gold

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

At what distance from a convex lens should an object be placed on the axis so as to form a real image of the same size? Illustrate your answer with a ray diagram.
Under what conditions does a concave lens form a real image?
Does the focal length of a lens change if it is immersed in water? Will it increase or decrease?
Draw the ray diagram showing the formation of a virtual image by a convex lens.
Can a concave lens form a real image? Give the condition.
Does the focal length of a lens change when immersed in water? Will it increase or decrease?
A lens made of glass is immersed into water. Will its power increase or decrease?
Draw the ray diagram showing the formation of real image by a concave lens.
If a converging lens and a diverging lens having the same focal length be in contact, how will the combination of lenses behave?

How does K.E. of an object change if its momentum is doubled?

Physics XI Notes — Sun, 18 Aug 2013 05:41:42 +0000

We have,

(K.E.)1= P²/2m

Where ‘P’ is momentum and ‘m’ is the mass of the object.
If the momentum is doubled then,

(K.E.)2 = (2P)²/2m

Or, (K.E.)2 = 4(K.E.)1

Therefore, on doubling the momentum, the K.E. of the body increases by four times its initial K.E.