In Hertz's experiment,the rods act as a/an ...... .

How are radio waves produced?

What was the primary difficulty in establishing the wave theory of light,and who explained it?

$A$ cylindrical region contains a uniform electric field that is along the cylinder axis and is changing with time. If $r$ is the distance from the cylinder axis,the magnitude of the magnetic field within the region is:

Match List-$I$ with List-$II$ and choose the correct answer from the options given below:
| List-$I$ | List-$II$ |
| :--- | :--- |
| $A. \oint \vec{B} \cdot d\vec{l} = \mu_0 i_c + \mu_0 \varepsilon_0 \frac{d\phi_E}{dt}$ | $I. \text{Gauss' law for electricity}$ |
| $B. \oint \vec{E} \cdot d\vec{l} = -\frac{d\phi_B}{dt}$ | $II. \text{Gauss' law for magnetism}$ |
| $C. \oint \vec{E} \cdot d\vec{A} = \frac{Q}{\varepsilon_0}$ | $III. \text{Faraday law}$ |
| $D. \oint \vec{B} \cdot d\vec{A} = 0$ | $IV. \text{Ampere-Maxwell law}$ |

According to Maxwell,a changing electric field produces .......