**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/R^{2}

**(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 π^{2} (l/T^{2})

**(xxi) Aim of the Simple Pendulum Experiment**

Ans: (a) To determine the acceleration due to gravity at the place.

(b) To draw l – T^{2} 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/T^{2} is calculated. In all cases it is found that (l/T^{2}) is a constant. The average value of (l/T^{2}) is determined and the acceleration due to gravity (g) is calculated. g = 4π2(l/T^{2})

**(b) To draw T ^{2} — l graph**

The experiment is performed as explained above. A graph is drawn with l along the X-axis and T^{2} 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 T^{2}= 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 T^{2} = 1.52 = 2.25 is determined from the graph.

(iii) From the graph, 1/T^{2} = AB/BC. Therefore, g = 4π^{2}(AB/BC)