^Weight, W
^Weight, W
Weight of a mass (called victim mass, m) at a place is equal to gravitational pull experienced by it at that place due to the gravitational field of a source mass (M). It is given by
^Atomic mass unit (u)
^Atomic mass unit (u)
^Contact force
^Contact force
Force that is due to physical contact between the interacting bodies is called a contact force e.g. push, pull, friction, tension, up-thrust.
^Bohr correspondence principle
^Bohr correspondence principle
According to this principle the quantum theory must give same result as classical theory in the appropriate classical limit.
^Field force
^Field force
A force that interacts without a physical contact is called a field force e.g. gravitational, electromagnetic.
^Limitations of Bohr’s theory
^Limitations of Bohr’s theory
- It is valid only for single electron system.
- Nucleus was taken as stationary but it also rotates about its own axis.
- Couldn’t explain fine structure of spectral line.
- Provides no information about the relative intensities of spectral lines.
- Provides no distribution of electrons in an atom.
- Fails to explain that why do the electrons move only in circular orbits.
- Bohr’s theory doesn’t explain the Zeeman effect (splitting up of spectral lines in magnetic field) & Stark effect (splitting up of spectral lines in electric field).
- Bohr’s theory doesn’t explain the doublets in the spectrum of the some atoms e.g. in sodium (5890 A0 & 5896 A0).
- Silent about the selection rules which governs the transitions.
- Use two theories
(i) Quantum (to explain the existence of stationary orbits) &
(ii) Classical (for motion of electrons in the orbits). These two theories essentially oppose each other.
^Fundamental forces
^Fundamental forces
Basic forces e.g. nuclear, electromagnetic, gravitational & weak.
^Free body diagram
^Free body diagram
FBD is a vector diagram showing all the forces acting on a particular system.
^Tangential force
^Tangential force
- A force acting along or opposite to velocity is called tangential force.
- A force acting along velocity increases speed with time.
- A force acting opposite to velocity decreases speed with time.
- Tangential force can’t change direction.
- The work done by a tangential force is positive if it causes an increase in the KE of a system & negative if there is a loss of KE.
^External force
^External force
- Any force acting outside the system selected is called external force.
- Only external force can accelerate a system.
- Force internal or external is a matter of selection of system. e.g. if we consider a system of earth & sun, then the gravitational force on earth by sun & that by sun on earth are internal, but if we consider the system earth only then the same gravitational force on earth becomes external force & accelerates earth around the sun.
