**Solutions: Option D**

You can view the video tutorial here or the written solutions below.

(You can click here to view another post on similar question where angle is given instead)

**Solutions: Option D**

You can view the video tutorial here or the written solutions below.

(You can click here to view another post on similar question where angle is given instead)

**Solutions:**

View the video on how the gauge works.

<p><a href=”https://vimeo.com/138991946″>fuel guage using ammeter and variable resistor</a> from <a href=”https://vimeo.com/user10931667″>evantoh</a> on <a href=”https://vimeo.com”>Vimeo</a>.</p>

As the fuel level drops, the float which stays on the fuel surface will descend. The rod which is attached to the float will turn clockwise about the pivot X. As the rod turns, the resistance on the variable resistor increases. This increases the resistance of the circuit. Hence the current flowing through the circuit will decreases, causing the needle to deflect more to the left, indicating towards E (empty). Thus the reading on the fuel gauge decreases.

**Solutions:**

(i) Both the fixed resistor and sensor are in series.

Total effective resistance Re = 5000 + 1000 = 6000 ohms

V = IR

12 = I x 6000

I = 0.0020 A

Hence potential across Y, V = IR (where I is constant in a series circuit)

= 0.0020 x 1000

= 2.0 V

(ii) When the temperature increases and the resistance of sensor Y decreases,** the total effective resistance of the circuit decreases**.

Since V = IR, where the R of the fixed resistor is a constant 5000 ohms, as current I increases, **the potential difference across the 5000 ohms resistor will increase.**

When a system is in **equilibrium**, 2 conditions are met.

**1) Principle of Moment (POM):**

Sum of anticlockwise moment = Sum of clockwise moment

**2) Net force = 0N; all forces are balanced:**

Total downward forces = Total upward forces

Whenever a force passed through the pivot point, that force will not create any moment as there is no perpendicular distance from the force to the pivot. Hence this force will not be included in the calculation of moments.