Physics Revision III
Sound and Modern Physics
- A pitcher under a tap of running water when gradually fills with water produces flat sounds at the beginning but gradually the sound becomes sharper. Why?
- All harmonics are overtones but all overtones are not harmonics
- What is the difference in the sound of same loudness and same pitch from a piano and a flute?
- Why does the guitarist rotate the pegs attached to the string in the guitar?
- Rumbling sound persists even after a thunder. Why?
- What is the minimum distance to hear the echo of the trisyllabic word “syllable”. Assume velocity of sound as 330m/sec?
- How does the frequency of sound emitted by flute changes?
- What is the audible range of sound?
- Why do buildings vibrate when a thunder falls nearby?
- Is the velocity of sound emitted from a violin different from that emitted from a piano?
- Time period of vibration of a body is .02 sec is the sound audible?
- A radio station sends 300m long radio waves. If the velocity of radio waves be 3x 10^8m/sec, find the frequency of radio waves.
- The average person can hear sound waves ranging in frequency from about 20 Hz to 20 kHz. Determine the wavelengths at these limits, taking the speed of sound to be 340 m/s.
- Of these properties of a wave, the one that is independent of the others is its_______
- The speed of waves in a stretched string depends upon which one of the following?
- The intensity of a sound wave is directly proportional to________
- What is the function of LT( low tension battery) in cathode ray tube?
- What is application of diode?
- What is eV? Is it unit of work or not?
- Which rule guides the deflection of electrons in a magnetic field?
- What decides the chemical properties of an element? Mass no. or atomic no. or no. of electron?
- Why are cathode rays deflected by magnetic fields?
- The radiation from a radioactive element passes through an electric field. What will happen?
- Is it possible to get gamma radiation without alpha and beta radiation in radioactive elements?
- Three molecules are: 17A35 , 17B37 , 15C35 ,identify isobar, isotone and isotope.
- Why helium gas is is found in radioactive mines?
- What will be the mass no and atomic no after the emission of two alpha particle and one beta particle from 92A235.
- Which among alpha, beta, and gamma have the highest ionizing power?
- Two isotopes of an element have _____
Answers to the above Questions
1. This is due to the change in effective length of the air column. In the beginning when the pitch is empty the sound wave formed in the pitcher spread almost through the whole volume of the pitcher, so the wavelength is sufficiently large. Pitch is thus low i.e. the sound is flat. As water fills the pitch, the air fills the pitcher, the air space slowly decreases. Thus wavelength decreases and the pitch increases i.e. the sound becomes more and more sharp.
2. In a note the least frequency is called fundamental tone and all other are called the overtones. Among the overtones those which are multiple of the fundamental tone are called the harmonics. E.g. in a note the frequencies are 200Hz, 300Hz, 400Hz, 475Hz, 550Hz,600Hz.
Among these 200 is the fundamental tone of the note. All others are overtones but the 3rd (400Hz) and the 7th (600Hz) are harmonics as they are multiple of the fundamental tone.
3. The difference is in the waveform.
4. By rotating the pegs he is changing the tension in the strings of guitar. The length of the strings remains the same but the change in tension changes the frequency.
5. The sound of a thunder gets reflected by clouds from various levels and so repetition of sound continues for along time. This is called rumbling of clouds.
6. 99m. (Hints: each syllable takes 1/5th sec)
7. In a flute there are holes. Air is blown in the flute and the by covering and uncovering of the holes we change the effective air column length, which gives the various frequencies.
8. 20Hz to 20,000 Hz
9. This occurs due to resonance. Usually the natural frequency of buildings is very high. But if a thunder falls very near a building, the sound emitted may resonate with the frequency of the building.
10. No. The velocity of sound is constant in the air if the temperature, pressure, and other physical conditions are same. Only waveform is different.
11. Yes as the frequency comes to be 50Hz.
13. 17 m, 1.7 cm
15.The tension in the string
16. The square of the amplitude.
1. It heats up the cathode so that thermionic emission can take place.
2. Current flows through the diode only when there is a negative potential at anode. If it is placed in an alternating current i.e. reversal of negative and positive occurs then the diode will cut off those which make the anode positive. So the outcome consists only those which keep the anode negative. So this acts as a filter or valve.
3. eV is a unit of work. 1 eV=1.6×10^-19 J
4. Flemings left hand rule
5. Atomic no.
6. Cathode rays consist of electron particles which are negatively charged. So they are deflected by magnetic field.
7. Alpha particles are positively charged, beta particles are negatively charged and gamma particle are uncharged. So in an electric field the alpha particle deflects towards the negative plate, the beta particle towards the positive plate while the gamma particle remains undeflected.
8. No it is not possible. Gamma rays occur when the daughter or the parent nucleus is in a state of excitation (i.e. contains excess energy).this excitation can be brought due to emission of a beta or an alpha ray. Gamma radiations accompany a beta or alpha emission.
9. Isobar= same mass no, 17A35 , 15C35
Isotope=same atomic no 17A35 , 17B37
Isotone=same no of neutrons 17B37 , 15C35
10. Alpha rays are charged helium particles given by 4He2. Due to alpha emission the charged helium particles are emitted. In contact with atmosphere they take the two electrons and turn into neutral helium atoms.
11. Mass no=227
13. The same number of protons but a different number of neutrons