(1) Data are stored in hard disk drives on the basis of magnetism.

(2) A motor is an essential part of an electrical fan, and all motors contain magnets since they use magnetism and electricity to induce motion.

(3) Moving parts of computers like the lens and the eject mechanism of optical disc drives require motors to enable their motion and thus, involve the use of magnets since all motors operate using magnets.

(4) They are used in speakers and headphones to produce sounds ..
Hope it helped ! pLZ mark it as brainiest :)
Data are stored in hard disk drives on the basis of magnetism. The surface of the disk is coated with magnetic material that consists of billions or even trillions of tiny magnets. Computer circuit components are able to process data in terms of whether current is present or not, represented by a 0 or 1. The north and south poles of the tiny magnets on the surface of hard disk drives can represent either 0s and 1s, making them perfect for computer data storage. An electromagnetic head is used to store data into these cells since an electromagnet can reverse its own polarity by reversing the direction of current flowing through it--enabling it to rearrange the polls of the tiny hard disk drive magnets. The same head can also read the data stored on the hard disk drive.