(a) What do you understand by the term 'ultrasonic vibration'?
(b) State three uses of ultrasonic vibrations.
(c) Name three animals which can hear ultrasonic vibrations.

What do you understand by the term 'infrasonic vibration"?

The equation for the vibration of a string, fixed at both ends vibrating in its third harmonic, is given by y = (0.4 cm) sin[(0.314 cm^-1) x] cos[f(600pis^-1)t] .(a) What is the frequency of vibration ? (b) What are the positions of the nodes ? (c) What is the length of the string ? (d) What is the wavelength and the speed of two travelling waves that can interfere to give this vibration ?

Mark the correct choice as : (a) Both assertion and reason are true and reason is the correct explanation of assertion. (b) Both assertion and reason are true but reason is not the correct explanation of assertion. (c) Assertion is true but reason is false. (d) Assertion is false but reason is true. (e) Both Assertion and reason are false.Reason : Sound is mechanical wave, which require medium to travel. Assertion : We cannot hear the sound produced by a vibrating pendulum. Reason : The frequency of the pendulum is very less.

"A good germ plasm collection is essential for the successful breeding programme of crop". This is a message given by an agricultural officer to the farmers of a village. a. What do you mean by germ plasm? b. What is the significance of a germ plasm in a successful breeding programme? c. Cite any three types of plant materials included in the germ plasm.

(a) What is meant by electric current ? Give its direction ? (b) Name and define its unit. (c ) Which instrument is used to measure the electric current ? How should it be connected in a circuit ?

Figure. gives a speed-time graph of a particle in motion along a constant direction. Three equal intervals of time are shown. In which interval is the average acceleration greatest in magnitude ? In which interval is the average speed greatest ? Choosing the positive direction as the constant direction of motion, give the signs of v and a in the three intervals. What are the accelerations at the points A, B, C and D ?