CBSE Physics Experiment - The velocity of a Pulse in Slinky

Introduction

Slinkies are typically composed of steel and are lengthy helical springs. It is resilient and has noticeable flexibility. When one end is stationary while the other is stretched and given a jerk at a right angle to its length, it produces transverse waves. When compressions are applied to the slinky's free end at regular intervals of time, longitudinal waves are created. 

Table of Content

• Aim

• Theory

• Procedure

• Observations

• Results 

Aim

To calculate the velocity at which a pulse will spread across a stretched string or slinky.

Apparatus Required

• A metre scale

• A slinky (helical spring)

• A stopwatch

Theory 

A pulse is a single disturbance that is formed suddenly and moves briefly from one free end to another (which can be fixed). Pulse velocity is the amount of space the pulse covers in one second. Therefore,

\[{\rm{pulse velocity(v) = }}\dfrac{{{\rm{distance travelled by the pulse(s)}}}}{{{\rm{time taken by the pulse(t)}}}}\]

\[v = \dfrac{s}{t}\]

Procedure

1. Measure the length of a spring or thread by tying one end to a solid support. Let's say P.

2. With the use of a metre scale, measure a distance of 1 m from point P and label that location as Q.

3. Permit one pupil to hold the slinky at point P with one end.

4. Stretch the slinky and have a different student bring it to point Q.

5. After stretching the slinky past point Q, the student will make a strong push back in the direction of point Q. At Q, the push ought to come to an end.

6. The slinky produces a pulse that moves toward point P before being reflected back toward point Q.

7. Start the stopwatch at the very instance when the first single pulse is made to the slinky and stop the stopwatch when the last pulse is shown.

8. Keep track of how much time (t) it took the pulse to go along the slinky's length.

9. Changing the number of pulses each time to notice the time (t), and recording the findings, repeat the experiment four to five times.

Observation

1. Length of the slinky = ______(in cm)

                                        = ______ (in m)

Least count of the stopwatch= _____(in seconds)

Results

Mean = ______ m/s

The velocity at which a pulse moved through the slinky = _______ m/s

Precautions

1. Slinky or string should be properly attached at one end with a sturdy support.

2. The string or slinky should be uniform in length, flexible, and without any mass.

3. When recording the time, extra care should be used because differences in time can cause the pulse velocity to increase.

4. The gap between subsequent pulses should be kept constant.

Lab Manual Questions

1. Describe the type of pulse that a stretched string produces. Is it longitudinal or transverse? Can a string or thread (an amateur's telephone) produce a longitudinal pulse?

Ans: A stretched string produces pulses that are transverse in nature. Yes, a string or thread can also produce longitudinal pulses.

2. Why do we favour using a longer string for the experiment?

Ans: The stretched thread or slinky produces a pulse at a very high speed. Therefore, it is challenging to calculate how long the pulse spends travelling along the known short length of string in a single motion. Therefore, it is preferable to carry out the experiment with a longer string.

3. You probably noted in this experiment that it is not advised to take the average speed of pulses calculated with varied string lengths when expressing the results for the speed of a pulse in a string. Why?

Ans: The square root of the mass per unit length of the stretched string determines the speed of a pulse (or wave) across it. As a result, it will be possible to see different values of pulse speed for various values of string length. Therefore, we are unable to use the speed that was calculated using the average of the varied string lengths.

4. What distinguishes a pulse from a wave?

Ans: 

Viva Questions

1. Explain wave-motion.

Ans: A wave is a disturbance that propagates through a medium when nearby particles are propelled into motion by the medium's constituent particles through the exchange of energy.

2. What is the aim of your experiment?

Ans: To ascertain the speed at which a pulse spread through a stretched string or slinky.

3. Explain pulse.

Ans: A pulse is a wave that results from a single disruption in a medium.

4. What kinds of waves need a medium to propagate?

Ans: Longitudinal wave

5. Display the wave's crest and trough using a diagram.

Ans:

The Crest and Trough

6. What position each turn of a slinky makes when it is stretched?

Ans: A slinky's individual turn will be assumed in an equilibrium or rest position when it is stretched.

7. Which physical quantity moves to the other end of a spring when the free end is jerked?

Ans: From one end to the other, energy flows.

8. Name a typical laboratory tool that can generate sound waves in the air.

Ans: Tuning fork

9. Describe a lab tool that can be used to study waves.

Ans: Slinky

10.  What kind of wave can you make with a slinky?

Ans: Transverse wave

Practical Based Questions

1. The physical property that will not change once a sound wave reflects is 

1. velocity 

2. wavelength 

3. frequency 

4. All of these.

Ans: D) All of the above

2. The speed of sound in air at room temperature is 345 m/s. The wavelength of sound produced in air by a tuning fork at a pure tone frequency of 1 kHz is: 

1. 345 m 

2. 0.345 m 

3. 3.45 m 

4. 34.5 m

Ans: B) 0.345

3. Which of the following factors does not affect the speed of pulse propagation in a slinky?

1. Slinky dimensions 

2. Slinky material 

3. Slinky temperature 

4. Size of the slinky

Ans: A) Slinky dimensions

4. The physical amount that goes along the length of a slinky or string when a pulse is sent through it is,

1. speed 

2. frequency 

3. wavelength 

4. energy.

Ans: D) Energy

5. To determine the pulse's velocity in a string, we must have:

1. only a measuring scale

2. only a stopwatch

3. both measuring scale and stopwatch

4. neither measuring scale nor stop watch

Ans: C) Both measuring scale and stopwatch

6. A sound wave travels 5 cm between compression and rarefaction. It has a wavelength of

1. 5 cm

2. 10 cm

3. 2.5 cm

4. 20 cm

Ans: B) 10 cm

7. Where will the pulse quickly reflect if it strikes the fixed end as in diagram A ?

The Pulse will be Reflected at the End of the Fixed End

1. (i)

2. (ii)

3. (iii)

4. (iv)

Ans: B) (ii)

8. In an experiment of measuring the pulse velocity through a stretched string, a student had to choose between, (i) thick silk string and thick cotton string, and (ii) stop clock and table clock

1. Thick silk string and stop clock

2. Thick silk strong and table clock

3. Thick cotton string and table clock

4. Thick cotton string and stop clock

Ans: D) Thick cotton strong and stop clock

9. On a rope with one end fixed, the wave pulse can be created by 

1. giving the other end a single jerk 

2. giving the other end several jerks 

3. giving continuous jerks 

4. either (A) or (B) or (C)

Ans: A) Giving the other end a single jerk

10. Shyamal was using a slinky to determine the wave's velocity. He questioned the teacher about how to use the spring's functions. The spring should be 

1. long, supple, and flexible

2. brief, supple, and adaptable

3. brief, tough, and flexible

4. lengthy, soft, but rigid 

Ans: A) long, supple, and flexible

Conclusion

Slinkies are long helical springs that are often made of steel. It is noticeably flexible and resilient. Transverse waves are created when two ends are stretched and jerked at a right angle to one another, with one end remaining stationary. Alternating between compressions and rarefactions. Longitudinal waves, for instance, are those that move along a compressed spring. When the periodic up-and-down motion of the medium's particles is perpendicular to the wave's direction of propagation, transverse waves are produced.