Question

The fixed resistance is called:
A) Rheostat
B) Resistor
C) Key
D) Key switch

Answer 1

Hint: A fixed resistance implies that the resistance of the device remains constant and cannot be changed. There are also variable resistances which have the provision for changing the resistance value of the device during an experiment.

Complete answer:
By fixed resistance, it is implied that the resistance value of the device remains constant and cannot be changed. Fixed resistances are offered usually by resistors.
On the other hand, there are also variable resistances. Variable resistance implies that the resistance value of the device can be changed according to our requirements usually by changing some other parameter upon which the resistance of the device depends. An example of a variable resistance is a rheostat.
Fixed as well as variable resistances have their own individual uses. Fixed resistances are used particularly to control and limit the current in a known circuit and to produce a specific amount of heat every time (in heating appliances) through the application of the heating effect of electric current.

Therefore, the correct answer is B) Resistor.

Note:
Students must not think that keys or switches can actually offer variable or fixed resistance. Their purpose is not to offer resistance but to complete or break a circuit. Usually, an ideal switch will have no resistance and will only serve the purpose of completing the circuit without affecting the flow of current or interfering with other parameters of the circuit in any way. Hence, students should not get confused and think that switches or key switches might be the correct answer thinking that they have heard that an open switch is equivalent to a circuit with infinite resistance.