Short Answer Typei) What is an echo?
ii) State two conditions for an echo to take place?
i) Echo is the sound heard after reflection from a distant obstacle after the original sound has stopped.
ii) Conditions for an echo to take place are:
a) Minimum distance between the source of the sound and the reflector in air must be 17 m.
b) As compared to the wavelength of the sound wave, size of the reflector must be large enough for an echo to take place.
i) Which particles are responsible for current in conductors?
(ii) To which wire of a cable in a power circuit should the metal case of a geyser
be connected?
(iii) To which wire should the fuse be connected?
(i) Name the transformer used in the power transmitting station of a power
plant.
(ii) What type of current is transmitted from the power station?
(iii) At what voltage is this current available to our household?
Arrange 
rays in ascending order with respect to their,
i) penetrating power
ii) lionising power
iii) biological effect
(i) In a cathode ray tube what is the function of anode?
(ii) State the energy conversion taking place in a cathode ray tube.
(iii) Write one use of cathode ray tube.
Long Answer Type(i) Name the phenomenon involved in tuning a radio set to a particular station.
(ii) Define the phenomenon named by you in part (i) above.
(iii) What do you understand by loudness of sound?
(iv) In which units is the loudness of sound measured?
A battery of emf 12 V and internal resistance 2 ohm is connected with two resistors A and B of resistance 4 ohm and 6 ohm respectively joined ins series.
Find:
i) Current in the circuit
ii) terminal voltage of the cell
iii) potential difference across 6 ohm resistor
iv) electrical energy spent per minute in 4 ohm resistor.
(i) Represent the change in the nucleus of a radioactive element when a 
particle is emitted.
(ii) What is the name given to elements with same mass number and different atomic number
(iii) Under which conditions does the nucleus of an atom tend to radioactive?
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