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Kirchhoff’s Laws – Example Circuits Kirchhoff’s 1st Law: The sum of the currents entering any point in a circuit is equal to the sum of the currents leaving that point (a consequence of the conservation of charge) Kirchhoff’s 2nd Law: In any closed loop in a circuit, the sum of the emf in the loop is equal to the sum of potential difference around that loop (a consequence of the conservation of energy) ADVICE: Beware of direction! When going around the loop, if you go through the power source from the negative (short) side to the positive (long) side then this is classed as a positive emf; if you go in the opposite direction through the power source, it is a negative emf. Use Kirchhoff’s Laws to calculate the currents flowing where indicated: 1. 6V 2. 3 REMEMBER: To calculate potential difference, multiply resistance by current (V = I × R) 6V 3 2 2 4V I I 3. 6V 4. 6V I1 3 I2 2 3 4V I3 I 6V 5. 6. I1 3 2 I3 © FradleyPhysics 2016 4V 2 4V 6V I1 3 I2 2 I3 4V I2 ADVICE: If you end up with a negative current – that is ok! It just means the current is flowing in the opposite direction to the arrow drawn