In a meter bridge experiment, for measuring unknown resistance 'S', the null point is obtained at a distance $$30 \mathrm{~cm}$$ from the left side as shown at point D. If R is $$5.6$$ $$\mathrm{k} \Omega$$, then the value of unknown resistance 'S' will be __________ $$\Omega$$.

A $$1 \mathrm{~m}$$ long copper wire carries a current of $$1 \mathrm{~A}$$. If the cross section of the wire is $$2.0 \mathrm{~mm}^{2}$$ and the resistivity of copper is $$1.7 \times 10^{-8}\, \Omega \mathrm{m}$$, the force experienced by moving electron in the wire is ____________ $$\times 10^{-23} \mathrm{~N}$$.

(charge on electorn $$=1.6 \times 10^{-19} \,\mathrm{C}$$)

A potentiometer wire of length $$300 \mathrm{~cm}$$ is connected in series with a resistance 780 $$\Omega$$ and a standard cell of emf $$4 \mathrm{V}$$. A constant current flows through potentiometer wire. The length of the null point for cell of emf $$20\, \mathrm{mV}$$ is found to be $$60 \mathrm{~cm}$$. The resistance of the potentiometer wire is ____________ $$\Omega$$.

Resistances are connected in a meter bridge circuit as shown in the figure. The balancing length $$l_{1}$$ is $$40 \mathrm{~cm}$$. Now an unknown resistance $$x$$ is connected in series with $$\mathrm{P}$$ and new balancing length is found to be $$80 \mathrm{~cm}$$ measured from the same end. Then the value of $$x$$ will be ____________ $$\Omega$$.