State Kirchhoff's first law.

1. (a)State Kirchhoff's first law.[1]
2. (b)The variations with potential difference V of the current I for a resistor X and for a semiconductor diode are shown in Fig. 6.1. [Figure 6.1]
3. (b)(i)Determine the resistance of the diode for a potential difference V of 0.60 V. resistance =[3]
4. (b)(ii)Describe, qualitatively, the variation of the resistance of the diode as V increases from 0.60 V to 0.75 V.[1]
5. (c)The diode and the resistor X in (b) are connected into the circuit shown in Fig. 6.2. [Figure 6.2] The cell has electromotive force (e.m.f.) E and negligible internal resistance. Resistor Y is connected in parallel with resistor X and the diode. The current in the cell is 9.3mA and the current in the diode is 7.5 mA.
6. (c)(i)Use Fig. 6.1 to determine E. E =[1]
7. (c)(ii)Determine the resistance of resistor Y. resistance[2]
8. (c)(iii)Calculate the power dissipated in the diode. power =[2]
9. (c)(iv)The cell is now replaced by a new cell of e.m.f. 0.50 V and negligible internal resistance. Use Fig. 6.1 to determine the new current in the diode. current[1]

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