Paper 2 Magnetic Fields Answers

Q1 Straight Wire Field Pattern

1. Concentric circles centred on the wire. [1]
2. Right-hand grip rule. [1]
3. For the same distance from the wire, field strength is proportional to current, so it doubles. [2]

Q2 Solenoid Field

1. Inside a long solenoid the field is strong, nearly uniform, and along the solenoid axis. [2]
2. Increase current, increase turns per unit length, or add/use a soft iron core. [2]
3. Soft iron has high magnetic permeability, so it substantially increases the flux density, and low retentivity, so it loses most of its magnetisation when the current is switched off. [2]

Q3 Magnetic Field Notation

1. Into the page. [1]
2. Each cross represents the same direction, and equal spacing indicates constant field magnitude. [2]
3. Dots, representing field out of the page. [1]