An electromagnetic plane wave has an electric field given by E = E₀ sin(kx – ωt). The symbols k and ω are known respectively, as _ and _.

Here are the solutions to the questions:

3. An electromagnetic plane wave has an electric field given by $E = E_0 \sin(kx - \omega t)$. The symbols $k$ and $\omega$ are known respectively, as _________ and _________.

In the standard equation for a sinusoidal wave, $y(x,t) = A \sin(kx - \omega t)$:

• $k$ is the wave number (or angular wave number), which is related to the wavelength $\lambda$ by $k = \frac{2\pi}{\lambda}$.
• $\omega$ is the angular frequency, which is related to the frequency $f$ by $\omega = 2\pi f$ and to the period $T$ by $\omega = \frac{2\pi}{T}$.

Comparing these definitions with the given options:

• A. wavelength and speed - Incorrect.
• B. wave number and period - $k$ is the wave number (correct). $\omega$ is the angular frequency, which is directly related to the period $T$. While not strictly "period" itself, it is the closest option describing the time-related characteristic of the wave.
• C. amplitude and angular frequency - Incorrect, $E_0$ is the amplitude, not $k$.
• D. phase velocity and radius - Incorrect.

Given the options, the most appropriate choice is B, acknowledging that "period" is used in relation to angular frequency.

The correct option is B.

$$\boxed{\text{B. wave number and period}}$$

4. What instrument is represented in the diagram below?

The diagram shows a circle with the letter 'A' inside it. This is the standard circuit symbol for an ammeter.

• A. An Amplifier (symbol is typically a triangle)
• B. A Galvanometer (symbol is typically a circle with 'G')
• C. An Ammeter (symbol is a circle with 'A')
• D. A Voltmeter (symbol is a circle with 'V')

The correct option is C.

$$\boxed{\text{C. An Ammeter}}$$

5. Three resistors $2 \Omega$, $3 \Omega$ and $5 \Omega$ are connected in parallel in an electric circuit. What is the total resistance in the circuit?

For resistors connected in parallel, the reciprocal of the total resistance ($R_{total}$) is the sum of the reciprocals of individual resistances:

$$\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}$$