**Solutions: C**

Alternatively, you may put values to work out using the 2 basic formulae of P = IV and V = IR. Refer the video below.

**Solutions: C**

Alternatively, you may put values to work out using the 2 basic formulae of P = IV and V = IR. Refer the video below.

**Lighting circuit**, in fact all circuits at home, should be connected in **parallel**.

*Reasons being*:

**When one bulb is spoilt or switched off, the rest of the bulbs can still function normally at normal brightness. **This is because the **potential difference** across each bulb in the branches **remains the same**.

Refer to series and parallel circuits summary.

If the lighting circuit is connected in **series**, when one bulb is spoilt or switched off, it will be an** open circuit** and **no current can flow** through the circuit. Hence **all the bulbs cannot function**.

Rules of Series and Parallel Circuits

To understand direct current (DC) circuits, the best way is to think in terms of river system.

Series Circuit

Parallel Circuit

Series and Parallel Circuit

Examples:

**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.**