Voltage is increased, i think.
The option stating that the observer must be placed within the focal length is false or not a necessary condition for magnification.
Explanation:
Lens are used for magnification provided the nature of the lens is known and by positioning the object at correct position. So the object should be placed in the focal point of the lens for perfect magnification, it can also be kept within the focal point or focal length. But the object should not be kept beyond the focal length of the lens.
So among the given options, the object and image should be on the same side of the lens for magnification is true. Then the nature of lens should be converging for magnification is also true. And the most important point that the object should be placed within the focal length of the lens is the most mandatory for obtaining magnification. So the option stating that the observer must be placed within the focal length is false or not a necessary condition for magnification.
Explanation:
Given that,
We need to calculate the decay constant
Using formula of decay constant
We need to calculate the number of 
nuclei
Where,
A= activity
ci = disintegration
Hence, This is the required solution.
Answer:
C
Explanation:
velocity = displacement (m) / change of time (s)
velocity = (400 + 300) / (100 + 400)
velocity = 1.4 m/s
