In a potentiometer experiment of a cell of emf 1.25 V gives balancing length of 30 cm. If the cell is replaced by another cell, balancing length is found to be 40 cm. What is the emf of second cell?

In a meter bridge circuit, resistance in the left hand gap is $2\Omega$ and an unknown resistance X is in the right hand gap as shown in Figure. The null point is found to be $40$cm from the left end of the wire. What resistance should be connected to X so that the new null point is $50$cm from the left end of the wire?

একটি মিটার ব্রিজের ডান ও বাম ফাঁকে  যথাক্রমে 6 Ω  ও 4 Ω রোধ আছে।সাম্য বিন্দুর অবস্থান কোথায়?