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.

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.

State the laws of flotation.

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

For a body floating freely in a liquid, the following laws, called laws of flotation, must be followed:
a) The weight of the body is equal to the weight of the displaced liquid.
b) The centre of gravity of the body and the centre of gravity of the displaced liquid are in same vertical line.

Explain why a coin placed on a cardboard covering a glass falls into the glass when the cardboard is pulled to one side?

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

Explain why a coin placed on a cardboard covering a glass falls into the glass when the cardboard is pulled suddenly to one side

Ans: Due to inertia of rest, the coin tends to be at rest.

Thermal Properties of Matter- Old is Gold

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

Which has more atoms: a kilogram of hydrogen or a kilogram of iron?
Molecules of different gases have equal average kinetic energies, provided their temperature is the same. Do these molecules have equal velocities also?
Outline the essential features of the kinetic theory of gases.
Why do you consider an ideal gas while formulating the pressure in the light of kinetic theory of gases?
Why does the cycle tube burst sometimes in summer?
At absolute zero temperature, why the kinetic energy is zero?
Under what conditions do the real gases obey more strictly the gas equation PV=RT?
Write the unit of the universal gas constant and give its physical meaning.
In the kinetic theory of gases, why do we not take into account the changes in gravitational potential energy of the molecule?
Absolute zero temperature is not zero energy temperature. Explain.
What are the characteristics of a gas to be an ideal?

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?

Viscosity-Old is Gold

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

Machine parts are jammed in cold days. Why?
During certain windstorm, light roofs are blown off, why?
Define viscosity. Does it depend on temperature?
When a smooth-flowing stream of water comes out of a faucet, it narrows as it falls. Explain why this happens.
Explain why a suction effect is experienced by a person standing close to the platform at a station when a fast train passes.
Why does a flag flutter on strong wind?

Refraction at plane surfaces- Old is Gold

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

Why do in summer, roads often appear to be covered with water when seen from a distance? Explain.
Why does a clear pool of water always appear to be shallower than it actually is?
Why does the sun look a little oval then it is at the horizon?
Why does diamond sparkle?
A ray of light in air strikes a glass surface. Is there a range of angles for which total internal reflection takes place?
Can total internal reflection be achieved if object originates in rarer medium? Explain with a diagram to justify your answer.
If a plane glass slab is placed on letter of different colours, then violet coloured letters appear more and more raised up. Why?

What is meant by the moment of a couple?

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

Moment of a couple is defined as the product of one of magnitude of two equal forces and the distance between these vectors. Two equal & opposite forces acting on the body forms the couple.

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.

Why is the bottom of a ship made heavy?

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

We know that for the stability of a floating body, the metacenter should always lie above C.G. of the body. So, the bottom of the ship is made heavy to lower its C.G. below the metacenter to keep it stable.