Which sensor produces an output signal which is proportional to the ambient level of illumination falling on it?

(a)  

Which sensor produces an output signal which indicates the level of ambient magnetic flux?

(a)  

Which sensor produces an output signal proportional to the concentration of a particular gas, e.g. oxygen in its surroundings?

(a)  

Which sensor produces an output signal that is proportional to the force per unit area that it experiences?

(a)  

Which sensor produces an output signal that is proportional the the amount of water in the surrounding material e.g. soil?

(a)  

Which sensor produces an output signal that is proportional the the amount of water vapour in the air surrounding it?

(a)  

Which sensor produces an output signal that is proportional to the acidity or alkalinity of the material or liquid it is in contact with?

(a)  

Which sensor produces a signal proportional to the amount of ambient infra red radiation falling on it?

(a)