A physical quantity is something which can be measured and whose measurement is necessary because all the laws of physics are given in terms of these physical quantities. The examples of physical quantity are mass, length, time, temperature, electric current, velocity , acceleration, force, work, weight,power, energy etc.
There are some quantities which cannot be measured and hence are not classified as physical quantities , for example, love, honesty, hatred etc
Thus a physical quantity is a quantity which can be measured.
Permanent magnet. An induced magnet would be created when a piece of iron (for example) is in contact with a magnet. Temporary magnets would be something like an electromagnet. Bar magnets are permanently magnetic unless we heat them or hammer them to cause their domains to loose alignment.
The period of the wave would be halved
