(20 12? Chengdu) Xiao Li designed a simple electronic rangefinder as shown in the figure. R is a resistance wire with uniform thickness, and the resistance per centimeter is 0.

The resistance of the resistance wire to be measured is R =U, I = 1.5V0.2A = 7.5ω,

The total resistance of the resistance wire is r = 2r = 2× 7.5Ω =15Ω;

The length of the resistance wire l = 15ω 0.5ω/cm = 30cm,

That is, before starting the measurement, put the metal slider P on one end of the resistance wire, and the maximum measurable distance is 30cm；;

(2) when the voltage is 2V, the resistance of the access circuit is r ′ = u′ i = 2v0.2a =10ω,

The object m is located at l' = 10ω 0.5ω/cm = 20cm,

So the object M moves to the left △ L = L'-12l = 20cm-15cm = 5cm;

(3) When the voltage representation number is 1V, the resistance of the access circuit is R "= U" I = 1V0.2A = 5ω,

The object m is located at l "= 5ω 0.5ω/cm =10cm,

So the object M moves to the right △ L =12l-L "=15cm-10cm = 5cm;

So choose BD.