4.6 Going Deeper: Enrichment & Exam Preparation

Electricity at Work Around You

One Current, Many Jobs The same current does utterly different jobs depending on the device. In a fan or mixer motor it’s the magnetic effect spinning the blades; in the iron, kettle and geyser it’s the heating effect warming things up; and the cell or battery quietly supplies it all through a chemical reaction. Spotting which effect a gadget uses is a great everyday-physics habit.

Quick Reference

Idea In one line
Magnetic effect A current produces a magnetic field around the wire
Magnetic field Region where the magnetic effect can be felt
Electromagnet Current-carrying coil acting as a magnet (stronger with iron core)
Stronger electromagnet More current, more turns, and/or an iron core
Reverse poles Reverse the current direction
Heating effect Resistance converts electrical energy to heat
Nichrome High resistance → used in heating elements
Voltaic cell Two metal electrodes + liquid electrolyte → current
Dry cell Zinc (−) container, carbon rod (+), paste electrolyte; single-use
Rechargeable battery Can be charged and reused (e.g. Li-ion)

Memory Tricks & One-Page Revision

Revision Card

  • Oersted (1820): current deflects a compass → current makes a magnetic field.
  • Electromagnet stronger by: more Cells, more Turns, iron Core. Reverse current → reverse poles.
  • Heating effect: more heat with higher resistance, more current, longer time, and the wire’s material/thickness/length.
  • Nichrome heats; copper carries. Heaters use nichrome because of its high resistance.
  • Cell parts: two electrodes (different metals) + electrolyte (acid/salt liquid or paste).
  • Dry cell: zinc = −, carbon rod = +, single-use. Rechargeable = Li-ion, reusable.
  • Earth is a magnet because moving molten iron makes currents in its core.

Spot the Mistake

Find the Flaw

  1. “An electromagnet using 1 cell lifts more clips than the same one with 2 cells.” — False: more cells → more current → stronger magnet → more clips.
  2. “Copper wire is used in heaters because it heats up the most.” — False: nichrome is used because it has higher resistance; copper barely heats.
  3. “A dry cell can be recharged like a phone battery.” — False: an ordinary dry cell is single-use; only rechargeable batteries can be recharged.

Test Your Reflexes

A quick-fire drill: a device or phenomenon appears. Which effect of electric current is it using — Magnetic or Heating? Build a streak!

Which effect is it?
Magnetic effect or heating effect?
Score 0 · Streak 0

Exam Corner: CBSE-Style Practice

Mixed Practice (objective, short, long, HOTS)

Objective type (1 mark each)

  1. The liquid used in a Voltaic cell is called the ______.
  2. A current-carrying coil that behaves like a magnet is called an ______.
  3. Nichrome is used in heaters because it has high ______.

Short answer (2 marks each)

  1. State two ways to increase the strength of an electromagnet.
  2. Why is a lifting electromagnet more useful than a permanent magnet in a scrapyard?

Long answer (3 marks each)

  1. Describe Activity 4.1 and explain what the deflection of the compass needle proves.
  2. Compare a Voltaic cell, a dry cell and a rechargeable battery — name the electrodes/electrolyte type and one key feature of each.

HOTS (Higher Order Thinking)

  1. A nichrome wire warms up and deflects a compass placed below it. Which effects are at work, and are both observations correct?
  2. Sumana forgets to switch off her lifting electromagnet; after a while it stops lifting clips, yet the coil is still warm. Give a likely reason.

Assertion–Reason (Choose: (a) both true, R explains A; (b) both true, R doesn’t explain A; (c) A true, R false; (d) A false, R true.)

  1. Assertion (A): Adding an iron nail inside a current-carrying coil makes it lift more clips.   Reason (R): An iron core strengthens the electromagnet’s magnetic field.
  1. electrolyte.
  2. electromagnet.
  3. resistance.
  4. Any two: use more cells (more current), wind more turns, add an iron core. (Reversing current changes poles, not strength.)
  5. It can be switched off to release the load (a permanent magnet cannot), and it can be made much stronger — ideal for lifting and dropping heavy scrap on command.
  6. A compass is placed under a wire in a simple circuit. With current ON, the needle deflects; with current OFF, it returns. This proves the current produces a magnetic field (the magnetic effect), which acts on the compass; the field vanishes when current stops.
  7. Voltaic cell: two different metal electrodes in a liquid electrolyte; first practical cell, but bulky. Dry cell: zinc (−) container + carbon rod (+) in a paste electrolyte; portable but single-use. Rechargeable battery: can be charged and reused many times (e.g. Li-ion).
  8. Both are correct: the wire shows the heating effect (it warms due to resistance) and the magnetic effect (the current deflects the compass) at the same time.
  9. The cell has likely run down (gone dead) — its chemicals are used up, so little or no current flows and the magnetism is too weak to hold clips. (Residual warmth can linger, and weak current still causes slight heating.)
  10. (a) — Both true and R explains A: the iron core strengthens the field, so the electromagnet lifts more clips.

Glossary

Key Terms

  • Magnetic effect of current: a current produces a magnetic field around a conductor.
  • Magnetic field: the region where a magnetic effect can be felt.
  • Electromagnet: a current-carrying coil that acts as a magnet; stronger with an iron core.
  • Heating effect of current: electrical energy converted to heat as current overcomes resistance.
  • Resistance: the opposition a conductor offers to the flow of current.
  • Heating element: the high-resistance coil/rod in a heating appliance.
  • Electrode / electrolyte: the metal rods / the conducting liquid (or paste) in a cell.
  • Voltaic cell, dry cell, rechargeable battery: three kinds of cell that make current by chemical reaction.