Which one of the following is the best shape of a solid metal rod to form the top end of a lightning conductor?
Which of the following forces is/are fundamental in nature?
1. Gravitational force
2. Electromagnetic forces
3. Strong and weak nuclear forces
Select the correct answer using the code given below :
1 only
1 and 2 only
2 and 3 only
1, 2 and 3
A spherical shell of outer radius R and inner radius R/2 contains a solid sphere of radius R/2 (see figure). The density of the material of the solid sphere is ρ and that of the shell is ρ/2. What is the average mass density of the larger sphere thus formed?
3ρ/4
9ρ/16
7ρ/8
5ρ/8
The human eye is like a camera that has a lens with :
fixed focal length and fixed aperture size.
variable focal length and fixed aperture size.
fixed focal length and variable aperture size.
variable focal length and variable aperture size.