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Q10 (Medium): Six cells A, B, C, D, E, and F are given to you. Cells A, B, D are good cells; cells C and E are dead cells; cell F is connected in the wrong direction. Which cells would you connect to get a brighter light from the lamp?
Answer:
We have studied that a
battery
is formed when cells are connected
positive-to-negative
.
Dead cells
provide no energy and
wrong-direction cells
cancel energy. So we use only good cells correctly.
- Cells A, B, D are good and working
- Cells C and E are dead — they provide no electrical energy
- Cell F is in the wrong direction — it opposes and reduces current
- Connect A, B, D in series (positive terminal of one to negative terminal of next) for brightest light
Conclusion: Connect cells A, B, and D in series. Never include dead (C, E) or reversed (F) cells.
Q11 (Difficult): Tanya made a circuit using an LED, a battery, and a switch. She finds the LED does not glow even when the switch is ON. What could be the reasons? How will she fix the circuit?
Answer:
We have studied that an
LED
works in
one direction only
— its
longer wire (positive)
must connect to the
positive terminal
of the battery. If connected the wrong way, the LED will NOT glow even in a working circuit.
- Reason 1: LED is connected in the wrong direction
- Reason 2: Battery is discharged or wrongly connected
- Reason 3: Loose or broken wire connection
- Reason 4: LED itself is damaged or fused
How to fix:
- Step 1: Reverse the LED — connect its longer wire (+) to the positive terminal of the battery
- Step 2: Check all wire connections for loose ends
- Step 3: Replace battery with a fresh one to rule out dead battery
- Step 4: Test with a different LED to check if original is damaged
Key Point: An LED is direction-sensitive (unlike a bulb). Always connect the LED's longer wire (+) to the battery's positive terminal.
