Science (086) — CBSE Class 10 board question

(i) Solenoid:
A solenoid is a long coil of wire consisting of a large number of closely wound circular turns of insulated copper wire.

Diagram:

```
N |====|====|====|====| S
→ → → → → → (field lines inside, parallel and uniform)
(curved lines emerge from N-pole and re-enter at S-pole outside)
```
Inside: uniform, parallel field lines (like a bar magnet).
Outside: field lines emerge from N-end, curve around, and enter S-end.

---

(ii) Two factors affecting the magnetic field of a solenoid:

1. Number of turns — more turns, stronger the field.
2. Amount of current flowing through the solenoid — more current, stronger the field.

---

(iii) Straight wire (solenoid stretched):
When a solenoid is stretched into a straight wire, the field consists of concentric circles centred on the wire.

```
↑ I
⊙ ← wire → ⊙ (circles around the wire; direction given by Right-Hand Thumb Rule)
```
Direction: Anticlockwise when viewed from the direction of current (Right-Hand Thumb Rule).

Source: Chapter 12, Sections 12.2 and 12.2.2

---

• (i): Examiners expect the definition (1 mark) + labelled diagram showing uniform parallel lines inside and curved lines outside, with N and S poles marked (1 mark).
• (ii): Any two from: number of turns, magnitude of current, presence of soft iron core. Write clearly as numbered points.
• (iii): Key point — a straight wire carrying current has concentric circular field lines (not parallel). You must state the direction rule (Right-Hand Thumb Rule) and ideally show arrows on the circles. This connects back to Activity 12.4 and the exercise question 1(d) in the chapter.