Answer :

a) The device used to change the alternating voltage to a higher or lower value is step up or step-down transformer. It works on the principle of Faraday's law of induction by converting one value of electrical energy into another.
One of the reasons for power dissipation in this device is the production of eddy currents in core. The changing magnetic field induces an EMF in the secondary winding. However, due to this changing magnetic field through the core, an EMF is induced in the core itself as the core is made of conducting material and thus current is generated in the core. These circulating currents are in the form of swirling eddies, called eddy currents. 

b) The relation between the voltage in the secondary coil with a voltage in the primary coil is given as

And the relation between current in the secondary coil with a current in the primary coil is given as

In a step-up transformer, if the voltage is getting stepped up, then current in the secondary coil is getting reduced.

Hence the power loss (P = I2R) is reduced considerably while such stepping up is not possible for direct current.

c) The teacher is well informed and willing to share her knowledge with Geeta that reflects her concerns for her. She wants her students to learn the practical aspects of the theoretical learning that is done in the class. 
Geeta, on the other hand, manifest the value of a good listener who is interested in learning the practical application of the concepts that has been taught in the class. It reflects her curious nature and the sheer willingness to learn something new. 

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