Simple Pendulum Viva Questions and Answers
(i) Who invented simple pendulum?
Ans: Galileo
(ii) Is `g' a vector quantity?
Ans: yes
(iii) What is the effective length of a simple pendulum?
Ans: It is the total length from the point of suspension to the centre of gravity of the bob
(iv) Why do we use heavy bob which is small in size?
Ans: A heavy bob has enough restoring force to overcome the air resistances. A small bob has less resistance due to air. So heavy bob, small in sizes is used as bob
(v) What is a seconds pendulum?
Ans: It is a simple pendulum whose time period is 2 seconds. It takes one second to move from one extreme position to the other end.
(vi) If the given bob is replaced by a wooden bob of the same size will the time period change?
Ans: It remains the same
(vii) What will happen to the time period if a simple pendulum is setup on the surface of the moon?
Ans: The time period will increase as the value of 'g' on the surface of the moon in less than that on the surface of the earth.
(viii) While oscillating, the amplitude of the pendulum must be small-why?
Ans: For small amplitude sin θ = θ in radians. Then the simple pendulum has simple harmonic oscillations.
(ix) What is the relation between 'g' and 'G'? Gin
Ans: g = Gm/R2
(x) What is the value of 'g' at the centre of the earth?
Ans: zero.
(xi) If you set up a simple pendulum in an artificial satellite orbiting the earth what will be the period of the pendulum?
Ans: Inside the satellite g = 0. Hence period is infinite.
(xii) What is meant by periodic motion?
Ans: A motion which repeats after equal intervals of time is called periodic motion.
(xiii) What is meant by amplitude?
Ans: It is the maximum displacement of a particle from its mean position.
(xiv) What happens if the bob of the simple pendulum has rotatory motion along with the translatory motion?
Ans: The rotatory motion will produce twist in the thread which changes the time period.
(xv) Define time period of an oscillating body.
Ans: It is the time taken by the oscillating body to complete one oscillation.
(xvi) Define frequency.
Ans: Number of periodic motions that occurs in unit time is called frequency of the periodic motion.
(xvii) How is frequency related to period of oscillation?
Ans: Period = 1/frequency
(xviii) How will the value of 'g' be affected if the earth stops rotating?
Ans: The value of 'g' would increase in general. The variation is maximum at the equator and minimum at the poles.
(xix) Apparatus of the Simple Pendulum
Ans: A simple pendulum, stop clock, metre scale, vernier calipers, stands etc. The simple pendulum consists of a metallic bob suspended by a light inextensible string passing through the split halves of a cork.
(xx) Theory of Simple Pendulum
Ans:The period of a simple pendulum of length l at a place where the acceleration due to gravity is g, which is given by,
T = 2π √(l/g);
Therefore, g = 4 π2 (l/T2)
(xxi) Aim of the Simple Pendulum Experiment
Ans: (a) To determine the acceleration due to gravity at the place.
(b) To draw l – T2 graph and hence to find the length and period of the Pendulum.
(xxii) Procedure of the Simple Pendulum Experiment
(a) To find the acceleration due to gravity at the place
The period of oscillation, T = (t/30), is calculated. The experiment is repeated with different lengths l (60, 70, 80 ………….. cm) of the pendulum. In each case l/T2 is calculated. In all cases it is found that (l/T2) is a constant. The average value of (l/T2) is determined and the acceleration due to gravity (g) is calculated. g = 4π2(l/T2)
(b) To draw T2 — l graph
The experiment is performed as explained above. A graph is drawn with l along the X-axis and T2 along the Y-axis. This graph is a straight line.
(i) To find the length of the seconds pendulum
A seconds pendulum is one for which the period of oscillation is 2 seconds. From the graph the length 1 corresponding to T2= 4 is determined. This gives the length of the seconds pendulum.
(ii) To find the length of the pendulum whose period is 1.5 seconds, the length l corresponding to T2 = 1.52 = 2.25 is determined from the graph.
(iii) From the graph, 1/T2 = AB/BC. Therefore, g = 4π2(AB/BC)