Home
Class 12
PHYSICS
A radioactive source of halflife 2 h emi...

A radioactive source of halflife 2 h emits radiation of intensity which is 64 times the permissible safe level. The minimum time in hours after which it would be possible to work safely with the source is:

A

12

B

8

C

6

D

24

Text Solution

Verified by Experts

Doubtnut Promotions Banner Mobile Dark
|

Topper's Solved these Questions

  • MODEL QUESTION PAPER 5

    SARAS PUBLICATION|Exercise EXERCISE|45 Videos

  • OPTICS

    SARAS PUBLICATION|Exercise EXAMPLE|46 Videos

Similar Questions

Explore conceptually related problems

A source S and a detector D are placed at a distance d apart. A big cardboard is placed at a distance sqrt2d from the source and the detector as shown in figure. The source emits a wave of wavelength = d/2 which is received by the detector after reflection from the cardboard. It is found to be in phase with the direct wave received from the source. By what minimum distance should the cardboard be shifted away so that the reflected wave becomes out of phase with the direct wave ?

A source emitting sound of frequency 180 Hz is placed in front of a wall at a distance of 2 m from it. A detector is also placed in front of the wall at the same distance from it. Find the minimum distance between the source and the detector for which the detector detects a maximum of sound. Speed of sound in air =360ms^-1 .

Knowledge Check

  • A freshly prepared radioactive sample of half-life 4 hours emits radiation of intensity which is 64 times the safe level. The minimum hours after which it would be safe to work with it is

    A
    4
    B
    6
    C
    12
    D
    24

    • Similar Questions

    Explore conceptually related problems

    A point source of monochromatic light of 1.0 mW is placed at a distance of 5.0 m from a metal surface. Light falls perpendicularly on the surface. Assume wave theory of light to hold and also that all the light falling on the circular area with radius =1.0 xx 10^-9m (which is few times the diameter of an atom) is absorbed by a single electron on the surface. Calculate the time required by the electron to receive sufficient energy to come out of the metal if the work function of the metal is 2.0eV .

    A certain radioactive material is known to decay at a rate proportional to the amount present. If initially there is 50 kg of the material present and after two hours it is observed that the material has lost 10% of its original mass, find () and expression for the mass of the material remaining at any time t, (ii) the mass of the material after four hours and (iii) the time at which the material has decayed to one half of its initial mass.

    A certain radioactive material is known to decay at a rate proportional to the amount present. If initially there is 50 kg of the material present and after two hours it is observed that the material has lost 10% of its original mass, find () and expression for the mass of the material remaining at any time t, (ii) the mass of the material after four hours and (iii) the time at which the material has decayed to one half of its initial mass.

    A metal block of heat capacity 90J//.^(@)C placed in a room at 25^(@)C is heated electrically. The heater is switched off when the temperature reaches 35^(@)C . The temperature of the block rises at the rate of 2^(@)C//s just after the heater is switched on and falls at the rate of 0.2^(@)C//s just after the heater is switched off. Assume Newton's law of cooling to hold (a) Find the power of the heater. (b) Find the power radiated by the block just after the heater is switched off. (c ) Find the power radiated by the block when the temperature of the block is 30^(@)C . (d) Assuming that the power radiated at 30^(@)C respresents the average value in the heating process, find the time for which the heater was kept on.

    Take a small stone. Hold it in your hand. We know that the force gravity due to the earth acts on each and every object. When we were holding the stone in our hand, the stone was experiencing this force, but it was balanced by a force that we were applying on it in the opposite direction. As a result, the stone remained at rest. Once we release the stone from our hands the only force that acts on it is the gravitational force of the earth and the stone falls down under its influence. Whenever an object moves under the influence of the force of gravity alone, it is said to be falling freely. Thus the released stone is in a free fall. In free fall, the initial velocity of the object is zero and goes on increasing due to acceleration due to gravity of the earth. During free fall, the frictional force due to air opposes the motion of the object and a buoyant force also acts on the object. Thus, true free fall is possible only in vacuum. For a freely falling object, the velocity on reaching the earth and the time taken for it can be calculated by using Newton's equations of motion. For free fall the initial velocity u=0 and the acceleration a=g . Thus, we can write the equations as v="gt",s=1/2"gt"^(2),v^(2)=2gs For calculating the motion of an object thrown upwards, acceleration is negative, i.e. in a direction opposite to the velocity and is taken to be -g. The magnitude of g is the same but the velocity of the object decreases due to -ve acceleration. The moon and the artificial satellites are moving only under the influence of the gravitational field of the earth. Thus they are in free fall. Which force acts on the stone in free fall after you release it?

    A monochromatic light source of power 5mW emits 8 xx 10^(15) photons per second. This light ejects photo electrons from a metal surface. The stopping potential for this set up is 2V. Calculate the work function of the metal.

    For the photoelectric emission from cesium, show that wave theory prodicts that (i) maximum kinetic energy of the photoelectrons (K_(max)) depends on the intensity I of the incident light (ii) K_(max) does not depend on the frequency of the incident light and (iii) the time interval between the incidence of light and the ejection of photoelectrons is very long. (Given : The work function for cesium is 1.90 eV and the power absorbed per unit area is 1.60 xx 10^(-6) Wm^(-2) which produces a measurable photocurrent in cesium.)

    Home
    Profile