Read the following passage and answer the accompanying questions - Leaving Cert Physics - Question 11 - 2017

The ampere is defined based on the force between two parallel conductors carrying current. When a current flows in two conductors placed 1 meter apart in a vacuum, they exert a force of 2 x 10^-7 N per meter. This demonstrates how the current carrying conductors interact in a magnetic field.

The Wheatstone bridge consists of four resistors arranged in a diamond shape with a galvanometer (or ammeter) connected across the middle. The resistors R1, R2, R3, and R4 should be clearly labelled, along with the galvanometer in the correct position to measure potential difference.

Telstar's orbit is geostationary, but the positioning of the satellite relative to Earth means that it does not remain in the same position relative to the ground. This results in limited time periods where it can transmit signals, not allowing for constant transmission.

Using the formula for gravitational force:

$T^2 = \frac{4\pi^2r^3}{GM}$

given that:

$T = 2.6 \times 60 \times 2$,

giving us a period of 312 seconds, we can rearrange this to solve for r:

$r = \left(\frac{T^2GM}{4\pi^2}\right)^{1/3}$

Substituting the known values:

$r = 9.6 \times 10^6 m$.

In optical fibres, light is transmitted through total internal reflection. The light hits the boundary at an angle greater than the critical angle, causing it to reflect back into the denser medium. A labelled diagram should show the fibre structure, the incident light, critical angle, and reflected light to illustrate this principle.

Using the relationship between distance, speed, and refractive index:

$v = \frac{c}{n}$

We can derive the refractive index from the speed of light and the speed of light in the glass. Given that light travels at a speed of 2/3 that of light in a vacuum, the refractive index is calculated as:

$n = \frac{c}{v} = 1.5.$

In telegraph cables, the communication is carried by electrons. In optical fibres, the communication is transmitted through photons.