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NDA Effects of Electric Current — practice questions — page 2

Explore 37 free Effects of Electric Current questions in NDA Science. Open each question or exercise to read its content, reference answers and available explanation.

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Effects of Electric Current questions and exercises with answers

Showing questions 31–37 of 37.

A short-circuit happens when:Read the answer and worked solution →An electromagnet differs from a permanent magnet in that the electromagnet:Read the answer and worked solution →Direction of force on a current-carrying conductor placed in a magnetic field is reversed if:Read the answer and worked solution →The Earth's magnetic field is roughly comparable to that of:Read the answer and worked solution →Frequency of AC in India is:Read the answer and worked solution →Fill the Ohm's-law blanksRead the answer and worked solution →Match each rule to what it givesRead the answer and worked solution →

Worked practice questions

A short-circuit happens when:

  1. Live and neutral wires touch directly
  2. Earth wire breaks
  3. Voltage is too low
  4. Insulation is too thick
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Correct answer: A. Live and neutral wires touch directly

1. Short-circuit: live and neutral wires come into direct contact (low-resistance path). 2. Current shoots up dramatically (I = V/R, R very small). 3. Generates intense Joule heat — fire hazard. 4. A correctly rated fuse should melt instantly and break the circuit. _Source: syllabus Science Ch 12 §12.8.1 Short-Circuit_

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An electromagnet differs from a permanent magnet in that the electromagnet:

  1. Is always weaker
  2. Loses its magnetism when current is switched off
  3. Has only one pole
  4. Cannot attract iron
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Correct answer: B. Loses its magnetism when current is switched off

1. An electromagnet is a soft-iron core inside a current-carrying coil. 2. Soft iron is easily magnetised but loses magnetism quickly when current stops. 3. Hence electromagnets can be turned ON/OFF — useful in cranes, electric bells, relays. 4. Permanent magnets (e.g., steel) retain magnetism on their own. _Source: syllabus Science Ch 12 §12.3 Electromagnet_

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Direction of force on a current-carrying conductor placed in a magnetic field is reversed if:

  1. Only the current is reversed
  2. Only the field is reversed
  3. Both current AND field are reversed
  4. Neither — the force is fixed
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Correct answer: C. Both current AND field are reversed

1. F = I L × B. Reversing either I or B reverses F. 2. Reversing BOTH simultaneously flips the sign TWICE — back to the original direction. 3. So the force is the SAME when BOTH are reversed (not the opposite). 4. Use Fleming's left-hand rule to verify. _Source: syllabus Science Ch 12 §12.4 Force on Current in Magnetic Field_

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