Question

How can a resistance box offer resistance by taking out the key?

Answer 1

resistance of any material depends upon
1. Length of material
2. cross section area of that material
3. resistivity of material.
because formula of resistance is
$R=\rho\frac{L}{A}$


now,
if the length of material is small then surely , resistance will be low and current flows through that material will be high.

and if the cross section area of material is small then, resistance will be low and current flows thought material will be high.

resistivity is the constant for specific material , we have to choose the material of low resistivity like silver , copper because these all metals have low resistivity , it means low resistance of these metal . hence, Current flows through these metals are high.

Answer 2

Often, the resistance box depends on the following: 1. Material's length 2. crossing section area 3. resistivity of material. when the length of a material is small, the resistance will be low and current that would flow through that material will be high.