कोई पदार्थ आवेशों के प्रवाह का कितना विरोध करता है, उसका माप (जो पदार्थ का एक अंतर्निहित गुण है) क्या कहलाता है?

The potential difference (V) between two points is defined as:

Which instrument is used to measure the potential difference between two points in an electric circuit?

Which law states that V = IR?