The root-mean-square (r.m.s.) value of the voltage of a sinusoidal alternating supply is 9.9 V. The frequency of the supply is 50 Hz. Derive an expression for the variation with time t (in second) of the potential difference V (in volt) of the supply.

1. (a)The root-mean-square (r.m.s.) value of the voltage of a sinusoidal alternating supply is 9.9 V. The frequency of the supply is 50 Hz. Derive an expression for the variation with time t (in second) of the potential difference V (in volt) of the supply.[2]
2. (b)Explain the function of the non-uniform magnetic field superposed on the large constant magnetic field in diagnosis using magnetic resonance imaging (NMRI).[3]
3. (c)A parallel beam of X-rays of intensity I₀ is incident normally on some soft tissue and bone, as illustrated in Fig. 10.1. [Figure 10.1] The bone is 0.40 cm thick and the total thickness of the bone and the soft tissue is 1.8 cm. The intensity of the transmitted beam is I. Data for the linear attenuation (absorption) coefficient µ of bone and of soft tissue are given in Fig. 10.2. [Figure 10.2] Calculate, in dB, the ratio transmitted intensity I / incident intensity I₀[4]