The potential difference applied across a given resistor is altered...

The potential difference applied across a given resistor is altered so that the heat produced per second increases by a factor of 9. By what factor does the applied potential difference change ?
\( \mathrm{P} \) In the figure shown, an ammeter A and a resistor of \( 4 \Omega \) are connected to the terminals of the source. The emf of the source is \( 12 \mathrm{~V} \) having an internal resistance of \( 2 \Omega \). Calculate the voltmeter and ammeter