Answer :

(c) The needle size determines the flow velocity, while thumb pressure determines the pressure. Bernoulli’s theorem states that P + 1/2pv2 = constant.

The pressure P has a single power in this equation, whereas the velocity has a square power. As a result, the velocity has a greater impact than the pressure. As a result, the syringe needle has better control over the flow rate than the doctor’s thumb pressure.