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Class 10 Magnetic Effects of Electric Current: cheat sheet
CBSE Science. A current makes a magnetic field, a magnetic field pushes on a current, and household wiring uses fuses and earthing to keep that current safe.
Key ideas
- Magnetic field lines go from the north pole to the south pole outside a magnet, never cross, and are closer where the field is stronger.
- Around a straight wire the field lines are circles; the right-hand thumb rule gives their direction (thumb along the current).
- The field is stronger nearer the wire and with a larger current.
- A solenoid behaves like a bar magnet: the field inside is uniform, and the end where the current looks anticlockwise is the north pole.
- A current in a magnetic field feels a force, greatest when the current is at right angles to the field; Fleming's left-hand rule gives its direction.
- Homes get 220 V between the live (red) and neutral (black) wires; the earth wire (green) is for safety. Appliances are connected in parallel.
- A fuse in the live wire melts if the current gets too large, from a short circuit or overloading.
Remember
| Fleming's left-hand rule | forefinger: field; middle finger: current; thumb: force |
| Right-hand thumb rule | thumb: current; curled fingers: field |
| Current drawn by an appliance | I = P ÷ V |
| Appliances in parallel | total current = total power ÷ 220 V |
Watch out
- Using the right hand for the force on a current (Fleming's rule uses the left hand).
- Forgetting that an electron moving one way is a current in the opposite direction.
- Putting the fuse in the neutral wire instead of the live wire.
Worked example
An electron enters a magnetic field pointing west, moving towards the south. In which direction is it pushed?
Working: the electron's motion is a current in the opposite direction; then Fleming's left-hand rule
Answer: Vertically upwards
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