Primary cells become unserviceable once discharged that is these can't be recharged while secondary cells can be chraged again and again.

It is to easy to magnetize and demagnetize the soft iron owing to its low retentivity and low coercivity.

Where low retentivity means that it becomes a weak magnet when the current is switched off.

and low coercivity means that it requires small opposite current to bring it back to the non-magnetic state.

As the x-rays are part of electromagnetic spectrum or in other words these are electromagnetic waves (EMW) so they have all the properties of EMW viz.

1. They don't require medium to travel or they can travel in space.

2.They travel in straight line

3. They travel with speed of light in space

4. They are consists of photons which are chargeless, massless quanta of enrgy so no deflection is observed in electric or magnetic field.

other wavelenght specific properties

5. X-rays produce illumination when falls on flourescent materials.

6. Photons of X-rays can ionise(ejecting outer orbits electron) the gases when x-rays pass through them.

7.X-rays can pass through flesh but not pass through bones that is their penetration capacity depends on material they strike. In genral penetration capacity decreases with wavelength that is higher wavelenght has weaker penetration capacity.

8.X rays has wavelength in range 1-100 Angstrom so possess high energy so can exhibit photo electric effect when strikes a photo sensitive material.

9.X-rays can kill cancerous cells so used in radiotherapy

When a pure semicondutor is doped with an impurity the impure semicondutor thus obtained is called extrinsic semicondutor.

P type extrinsic semicondutor- When the impurity is of acceptor type (trivalent(4 minus 1) elements such as aluminium, boron, gallium etc), the extrinsic semiconductor is said to be of p-type as the majority carriers are holes which are positive in nature.

N type extrinsic semicondutor-When the impurity is of donor type (pentavalent(4 plus 1) elements such as arsenic, antimony,phosphorus etc) the extrinsic semiconductor is said to be of n-type as the majority carriers are electrons which are negative in nature.