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Olympiad (Class 7) Electric current and its effects — practice questions — page 2

Explore 65 free Electric current and its effects questions in Olympiad (Class 7) Science. Open each question or exercise to read its content, reference answers and available explanation.

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Electric current and its effects questions and exercises with answers

Showing questions 31–60 of 65.

An iron core placed inside an electromagnet coil mainly:Read the answer and worked solution →A key advantage of an electromagnet over a bar magnet is that its magnetism can be:Read the answer and worked solution →A coil electromagnet is switched off. What happens to its magnetism?Read the answer and worked solution →A scrapyard crane drops its iron load by:Read the answer and worked solution →Which of these devices uses an electromagnet?Read the answer and worked solution →Maglev trains float above their track by using:Read the answer and worked solution →Magnetic separation equipment sorts scrap into parts that are:Read the answer and worked solution →Volta built the first electrochemical battery, the voltaic pile, in which year?Read the answer and worked solution →Volta's pile was a stack of copper and zinc plates separated by:Read the answer and worked solution →Who first used the word battery in 1749 for linked Leyden jars?Read the answer and worked solution →A cell that is used once and then thrown away is called a:Read the answer and worked solution →Which of these is a rechargeable (secondary) battery?Read the answer and worked solution →In a working battery, electrons leave through which terminal?Read the answer and worked solution →A cell that has a liquid electrolyte is called a:Read the answer and worked solution →Current flows in a circuit only when the circuit is:Read the answer and worked solution →Why does a bulb glow almost at once when the switch is closed?Read the answer and worked solution →Which of these is a natural example of electric current?Read the answer and worked solution →In nerve cells, an electric current is the flow of:Read the answer and worked solution →The symbol I for current comes from which French phrase?Read the answer and worked solution →André-Marie Ampère gave his name to the unit of:Read the answer and worked solution →A rapidly oscillating current in an antenna produces:Read the answer and worked solution →A changing magnetic field applied to a conductor can start:Read the answer and worked solution →A charge of 60 C flows past a point in 20 s. What is the current?Read the answer and worked solution →A current of 0.5 A flows for 4 minutes. How much charge passes?Read the answer and worked solution →A 5 ohm heater coil carries 2 A. What is the potential difference across it?Read the answer and worked solution →A 12 V source sends 0.5 A through a resistor. What is its resistance?Read the answer and worked solution →For a fixed resistor, if the voltage across it rises, the current:Read the answer and worked solution →In metallic solids, electric charge flows by means of:Read the answer and worked solution →In a metal wire, the positively charged atomic nuclei are:Read the answer and worked solution →Current can be measured without breaking the circuit by detecting its:Read the answer and worked solution →

Worked practice questions

An iron core placed inside an electromagnet coil mainly:

  1. Stops the current
  2. Cools the wire down
  3. Reduces coil weight
  4. Concentrates the field
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Correct answer: D. Concentrates the field

A magnetic core such as iron gathers the magnetic flux, making the magnet stronger.

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A key advantage of an electromagnet over a bar magnet is that its magnetism can be:

  1. Never altered at all
  2. Controlled by current
  3. Made without any wire
  4. Kept without a cell
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Correct answer: B. Controlled by current

Changing the current quickly changes the field, which a permanent magnet cannot do.

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A coil electromagnet is switched off. What happens to its magnetism?

  1. It slowly doubles
  2. It stays for ever
  3. It vanishes at once
  4. It slowly reverses
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Correct answer: C. It vanishes at once

The field exists only while current flows, so it vanishes when the current is turned off.

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