Define the ohm.

1. (a)Define the ohm.[1]
2. (b)A wire has a resistance of 1.8Ω. The wire has a uniform cross-sectional area of 0.38 mm² and is made of metal of resistivity 9.6 × 10⁻⁷Ωm. Calculate the length of the wire.[3]
3. (c)(i)A resistor X of resistance 1.8Ω is connected to a resistor Y of resistance 0.60Ω and a battery P, as shown in Fig. 5.1. [Figure 5.1] The battery P has an electromotive force (e.m.f.) of 1.2V and negligible internal resistance. Explain, in terms of energy, why the potential difference (p.d.) across resistor X is less than the e.m.f. of the battery.[1]
4. (c)(ii)Calculate the potential difference across resistor X.[2]
5. (d)(i)Another battery Q of e.m.f. 1.2V and negligible internal resistance is now connected into the circuit of Fig. 5.1 to produce the new circuit shown in Fig. 5.2. [Figure 5.2] State whether the addition of battery Q causes the current to decrease, increase or remain the same in: resistor X[1]
6. (d)(ii)battery P.[1]
7. (e)(i)The circuit shown in Fig. 5.2 is modified to produce the new circuit shown in Fig. 5.3. [Figure 5.3] Calculate: the total resistance of the two resistors connected in parallel[1]
8. (e)(ii)the current in resistor Y.[2]

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