Physics-18 Electromagnetic induction

A current produces a ​ (a)   . However, the reverse is also possible: a 

magnetic field can be used to produce a ​ (b)   .

• magnetic field

• current

• wire

• motor

Answer explanation

A current produces a magnetic field, demonstrating the relationship between electricity and magnetism. Conversely, a magnetic field can induce a current, highlighting the duality of these phenomena.

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A(n) ___ converts magnetism into electricity.

• electric transformer

• electric generator

• electromagnet

• electric motor

Answer explanation

An electric generator converts magnetism into electricity by using electromagnetic induction. It generates electrical energy from mechanical energy, making it the correct choice for this question.

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Electric charges must ___ in order to create an observable magnetic field.

• exist

• be moving

• be stationary

• disappear

Answer explanation

Electric charges must be moving to generate a magnetic field, as per Ampère's law. Stationary charges create no magnetic field, while moving charges (currents) do, making 'be moving' the correct choice.

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Which of the following will increase the strength of an electric generator?

• Use a Bigger Magnet

• Move the Magnet Slower

• Wrap More Coils

• Use a Bigger Battery

Answer explanation

Using a bigger magnet increases the magnetic field strength, enhancing the generator's output. Wrapping more coils increases the amount of wire in the magnetic field, also boosting the generated voltage. Both choices strengthen the generator.

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In Fleming's Right Hand Rule, First finger and center finger represent

• current, magnetic field

• magnetic field, current

• force, current

• magnetic field, force

Answer explanation

In Fleming's Right Hand Rule, the first finger represents the magnetic field, while the center finger represents the current. Therefore, the correct answer is 'magnetic field, current'.

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How can the size of the induced potential difference be increased? (more than one answers)

• Increase the speed of the movement

• Increase the number of coils

• Increase the current

• Use a bigger magnet

• Use a stronger magnet

Answer explanation

The induced potential difference can be increased by increasing the speed of movement, adding more coils, or using a stronger magnet. These factors enhance the magnetic flux change, leading to a higher induced voltage.

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Most of our ​ (a)   comes from huge ​ (b)   in power stations. There are smaller generators in cars and on some bicycles. These are called ​ (c)   .​

• electricity

• generators

• dynamos

• motors

Answer explanation

The first blank is filled with 'electricity' as it is generated in power stations. The second blank is 'generators', which produce electricity. The third blank is 'dynamos', a type of generator found in smaller applications like cars and bicycles.

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There are four ways of increasing the voltage generated by an a.c. generator like the one shown in:

◆ turn the coil ​ (a)  

◆ use a coil with ​ (b)   of wire

◆ use a coil with a ​ (c)  

◆ use ​ (d)  

• more rapidly

• more turns

• bigger area

• stronger magnets

• weakermagnets

• less turns

• less rapidly

• fewer turns

Answer explanation

To increase voltage in an a.c. generator, use stronger magnets for a greater magnetic field, a bigger area for more flux, more turns of wire to increase induced voltage, and turn the coil more rapidly to enhance the frequency of induction.

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​ (a)   may be 100 km or more from the places where the electricity they generate is used. ​ (b)   leaves the power station. Its ​ (c)   may be as much as ​ (d)   .​

• Power stations

• High voltage electricity

• voltage

• one million volts

• Buses

• ohms

• lowvoltageelectricity

• one hundred volts

Answer explanation

Power stations generate electricity, which is transmitted as high voltage electricity to minimize energy loss over long distances. This voltage can reach up to one million volts, ensuring efficient delivery to users.

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When the power lines ​ (a)   the area where the power is to be used, they enter a ​ (b)   . Here the ​ (c)   is reduced to a less hazardous level. In the substation, ​ (d)   reduce the voltage to the local supply voltage, typically ​ (e)   .​

• approach

• local substation

• voltage

• transformers

• 220-230 V

• 25-30Volts

• depart

• ohms

Answer explanation

When the power lines approach the area, they enter a local substation. Here, the voltage is reduced to a less hazardous level. Transformers in the substation typically reduce the voltage to 220-230 V for local use.

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