Circuit 1: Two cells and two bulbs with a toggle switch to turn the circuit on and off.

Let's go through each circuit and answer the questions step by step, using basic principles of electricity.

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Circuit 1: Two cells and two bulbs in series with a toggle switch

Circuit Description:
- Two cells (batteries) are connected in series → increases voltage.
- Two bulbs are connected in series.
- A toggle switch controls the circuit.

Question: *What happens if you unscrew one bulb?*

#### ✔ Answer:
If you unscrew one bulb, the entire circuit is broken, and both bulbs will go out.

#### 🔍 Explanation:
In a series circuit, the current has only one path to follow. When you unscrew one bulb, you break the circuit at that point — there is no complete loop for the current to flow. Since the current stops flowing entirely, neither bulb will light up.

This is a key feature of series circuits: if one component fails or is removed, the whole circuit stops working.

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Circuit 2: Two cells, one bulb, a 10 Ω resistor, and a switch

Circuit Description:
- Two cells in series → higher voltage.
- One bulb.
- A 10 Ω resistor.
- A switch.

All components are connected in series.

Question: *What happens to the brightness of the bulb if you remove the resistor from the circuit? Try to explain what you see, using ideas about resistance, energy, and current.*

#### ✔ Answer:
The bulb becomes brighter when you remove the resistor.

#### 🔍 Explanation:

Let’s use concepts of resistance, current, and energy:

1. Resistance in the circuit:
- The 10 Ω resistor adds total resistance to the circuit.
- When you remove it, the total resistance decreases.

2. Current (from Ohm’s Law):
- Ohm’s Law: \( I = \frac{V}{R} \)
- Voltage (V) stays the same (from the two cells).
- Resistance (R) decreases → so current (I) increases.

3. Brightness of the bulb:
- Brightness depends on how much power the bulb uses.
- Power: \( P = I^2 R_{\text{bulb}} \) → more current means more power → brighter bulb.

4. Energy transfer:
- With less resistance, more current flows → more electrical energy is transferred to the bulb per second → more light and heat produced → increased brightness.

5. Safety note:
- Removing the resistor can make the current too high, possibly damaging the bulb or causing overheating.

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✔ Summary:

| Circuit | What Happens? | Why? |
|--------|----------------|------|
| Circuit 1 | Both bulbs go out when one is unscrewed | Series circuit – breaking one part breaks the whole loop |
| Circuit 2 | Bulb becomes brighter when resistor is removed | Lower resistance → higher current → more power → brighter bulb |

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