A battery supplies 0.9 A current through a $2 \Omega$ resistor and 0.3 A current through a $7 \Omega$ resistor when connected one by one. The internal resistance of the battery is

A galvanometer of resistance $50 \Omega$ is converted into a voltmeter of range $(0-2 \mathrm{~V})$ using a resistor of $1.0 \mathrm{k} \Omega$. If it is to be converted into a voltmeter of range ( $0-10 \mathrm{~V}$ ), the resistance required will be

A current of 0.8 A flows in a conductor of $$40 \Omega$$ for 1 minute. The heat produced in the conductor will be

A cell of emf $$E$$ is connected across an external resistance $$R$$. When current '$$I$$' is drawn from the cell, the potential difference across the electrodes of the cell drops to $$\mathrm{V}$$. The internal resistance '$$r$$' of the cell is