You rub a rod of glass with a cotton cloth, then dip the cloth into a faraday pail

negative charge

Explanation:

As the glass rod is rubbed with the cotton cloth, then the glass rod becomes positively charged and the cotton cloth becomes negatively charged.

There is a tendency to lose the electrons by the glass rod and to grab the electrons by the cotton cloth.

So, the sensor shows negative charge.

Move the fulcrum 2 meters away from the side on which the force is applied.

Explanation:

The mechanical advantage of a lever is given by:

where

Fout is the output force

Fin is the input force

a is the distance between the point of application of the input force and the fulcrum

b is the distance between the load (output force) and the fulcrum

In this problem, we have a lever of total length 12 m. Initially, the fulcrum is exactly at the center of the lever, so

And so the mechanical advantage is

In order to double the MA, the value of a (distance between the input force and the fulcrum) must be twice that of b (distance between the load and the fulcrum):

We also know that

So, the solution to this system is

which corresponds to the following option:

Move the fulcrum 2 meters away from the side on which the force is applied.

(which means increasing a from 6 meters to 8 meters)