The typical transfer characteristics of a transistor in CE configuration is shown in figure. A load resistor of $$2 \,k \Omega$$ is connected in the collector branch of the circuit used. The input resistance of the transistor is $$0.50 \,\mathrm{k} \Omega$$. The voltage gain of the transistor is ______________.

Three point charges of magnitude $$5 \mu \mathrm{C}, 0.16 \mu \mathrm{C}$$ and $$0.3 \mu \mathrm{C}$$ are located at the vertices $$A, B, C$$ of a right angled triangle whose sides are $$A B=3 \mathrm{~cm}, B C=3 \sqrt{2} \mathrm{~cm}$$ and $$C A=3 \mathrm{~cm}$$ and point $$A$$ is the right angle corner. Charge at point $$\mathrm{A}$$ experiences ____________ $$\mathrm{N}$$ of electrostatic force due to the other two charges.

In a coil of resistance $$8 \,\Omega$$, the magnetic flux due to an external magnetic field varies with time as $$\phi=\frac{2}{3}\left(9-t^{2}\right)$$. The value of total heat produced in the coil, till the flux becomes zero, will be _____________ $$J$$.

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 ____________ $$\Omega$$.