The root-mean-square (r.m.s.) voltage of a sinusoidal alternating supply is $9.9\,\text{V}$. Its frequency is $50\,\text{Hz}$. Derive an expression for how the potential difference $V$ (in volt) varies with time $t$ (in second) for the supply.
Explain the role of the non-uniform magnetic field placed on top of the large constant magnetic field in diagnosis using magnetic resonance imaging (NMRI).
A parallel X-ray beam of intensity $I_0$ falls normally on soft tissue and bone, as shown in Fig. 10.1. The bone has a thickness of $0.40\,\text{cm}$, while the combined thickness of the bone and soft tissue is $1.8\,\text{cm}$. The intensity of the beam after transmission is $I$. Figure 10.2 gives the linear attenuation (absorption) coefficient $mu$ for bone and for soft tissue. Calculate, in dB, the ratio $\dfrac{\text{transmitted intensity } I}{\text{incident intensity } I_0}$.