SHM (Simple Harmonic Motion) is one of the key concept areas in the subject and is also an area where students are known to commonly acquire Misconceptions. Below is the list of concept and misconception than can avoid easily.
- Concept: Necessary and sufficient condition of S.H.M. is that the restoring force is proportional to displacement.
Misconception: Necessary and sufficient of S.H.M. is that force is proportional to displacement.
- Concept: In S.H.M., the average kinetic energy is equal to average potential energy if average is taken over a complete period and the potential energy in resting position is zero.
Misconception: In S.H.M., kinetic energy is equal to potential energy.
- Concept: In S.H.M. of amplitude A, the time (t1) taken to traverse from x = 0 to A/2 is less than the time (t2) taken from x = A/2 to A, because the velocity of particle at mean position is maximum at it goes on decreasing towards extreme position is maximum at it goes on decreasing towards extreme position. In fact, t1= t2/2.
Misconception: In S.H.M. of amplitude A, the time taken to traverse from x = 0 to A/2 and from x = A/2 to A is the same.
- Concept: The motion of particle executing uniform circular path is not S.H.M.; but the motion of projection of perpendicular drawn from instantaneous positions of particle executing uniform circular motion is S.H.M.
Misconception: The motion of particle executing uniform circular path is S.H.M.
- Concept: The time period of S.H.M. does not depend upon the amplitude or energy or phase constant.
Misconception: The time period of S.H.M. depends on amplitude, energy and phase constant.
- Concept: A combination of two simple harmonic motions of same frequency is simple harmonic motions of the same frequency is simple harmonic.
Misconception: A combination of any two simple harmonic motions is simple harmonic.
- Concept: The time period of a simple pendulum does not depend upon mass, but depends on the size of bob; because by increasing size of bob, the effective length of pendulum increases.
Misconception: The time period of a simple pendulum does not depend upon size and mass of bob.
- Concept: When a spring of spring constant K is divided into n equal parts, the spring constant of each part increases to nK.
Misconception: When a spring of spring constant K is divided into n equal parts, the spring constant of each part reduces to K/n.
- Concept: The time period of a mass-spring system remains same everywhere.
Misconception: The time period of a mass-spring system in artificial satellite is infinite.
- Concept: In damped simple harmonic motion, the amplitude of oscillations falls exponentially.
Misconception: In damped simple harmonic motion, the amplitude of oscillations falls linearly.
- Concept: In forced oscillations, the amplitude at resonance is infinite in the absence of damping.
Misconception: In forced oscillations, the amplitude at resonance is finite in the absence of damping
- Concept: In forced oscillations, the amplitude resonance occurs at a slightly lower frequency than the natural frequency of oscillations of the body while the velocity (or energy) resonance occurs when the frequency of driving force is equal to the natural frequency of oscillations of the body.
Misconception: In forced oscillations, the amplitude resonance and velocity (or energy) resonance occurs at the same driving frequency of force which is equal to the frequency of free oscillations of the body.
- Concept: Speed of sound in a vacuum is zero.
Misconception: Speed of sound in a vacuum is maximum.
- Concept: Traverse waves cannot propagate through gases.
Misconception: Transverse waves can propagate through gases.
- Concept: In the air the changes during passage of compressions and rarefactions are adiabatic.
Misconception: In the air the changes during passage of compressions and rarefactions are isothermal.
- Concept: The speed of longitudinal sound waves in solids is maximum.
Misconception: The speed of sound is minimum in solids and maximum in gases.
- Concept: At a given temperature the speed of sound in a gas is independent of pressure.
Misconception: At a given temperature, the speed of sound in a gas depends on pressure and is proportional to the square root of pressure.
