IB Physics HL: Electromagnetic Induction and AC Generators

1. Describe the emf induced in a coil rotating within a uniform magnetic field.

The induced emf is constant regardless of the speed of rotation.

The induced emf is proportional to the square of the speed of rotation.

The induced emf is triangular in shape if the rotation is at a constant speed.

Students should understand, without any derivation, that the induced emf is sinusoidal if the rotation is at constant speed.

Explanation

Students should understand, without any derivation, that the induced emf is sinusoidal if the rotation is at constant speed.

2. 12.2.2 Explain the operation of a basic alternating current (ac) generator.

The operation of a generator is similar to that of a light bulb in terms of energy generation.

A generator operates by using direct current to produce electrical energy.

In a generator, electricity is stored in a battery for later use.

3. Describe the effect on the induced emf of changing the generator frequency.

The induced emf increases with decreasing frequency of the generator.

Students will be expected to compare the output from generators operating at different frequencies by sketching appropriate graphs.

The induced emf decreases with increasing frequency of the generator.

The induced emf remains constant regardless of the generator frequency.

When changing the generator frequency, the induced emf is affected and students should be able to compare the outputs from generators at different frequencies through graph sketches.

Explanation

When changing the generator frequency, the induced emf is affected and students should be able to compare the outputs from generators at different frequencies through graph sketches.

4. What is meant by the root mean squared (rms) value of an alternating current or voltage?

The rms value is a mathematical average of the current or voltage values over a period of time.

The rms value is the peak value of the current or voltage waveform.

The rms value represents the maximum possible power that can be delivered by the alternating current or voltage.

The rms value of an alternating current (or voltage) is not the peak value or a mathematical average. It specifically refers to the value that dissipates power in a resistor at the same rate.

Explanation

The rms value of an alternating current (or voltage) is not the peak value or a mathematical average. It specifically refers to the value that dissipates power in a resistor at the same rate.

5. State the relation between peak and rms values for sinusoidal voltage and currents

Peak value is half of the rms value

See image.

Peak value is equal to the rms value

Peak value is double the rms value

The peak value of a sinusoidal voltage or current is equal to the square root of 2 times the rms value.

Explanation

The peak value of a sinusoidal voltage or current is equal to the square root of 2 times the rms value.

6. Outline the reasons for power losses in transmission line and real transformers

Powerloss in transmission line:Heatloss due to currentResistanceof the metal usedDielectriclossesSelf-inductance Powerloss in real transformers:EddycurrentsResistanceof the wire in the windingHysteresisPhysicalVibrationDielectriclossesElectromagneticradiationFluxleakage

Voltage regulation

Capacitor losses

Magnetic saturation

Voltage regulation, magnetic saturation, and capacitor losses are not main reasons for power losses in transmission lines and real transformers.

Explanation

Voltage regulation, magnetic saturation, and capacitor losses are not main reasons for power losses in transmission lines and real transformers.

7. Explain the use of high-voltage step-up and step-down transformers in the transmission of electrical power.

Step-up transformers are used to decrease voltage for more efficient power transfer.

High-voltage step-down transformers are not necessary in the transmission of electrical power.

There is an ideal value of step-up voltage for electrical transmission.

The correct answer explains the process of using step-up and step-down transformers in electrical power transmission, highlighting the increase and decrease in voltage to optimize power transfer efficiency.

Explanation

The correct answer explains the process of using step-up and step-down transformers in electrical power transmission, highlighting the increase and decrease in voltage to optimize power transfer efficiency.

8. How do extra-low-frequency electromagnetic fields induce currents within a body?

Extra-low-frequency electromagnetic fields directly cause muscle contractions within the body.

Extra-low-frequency electromagnetic fields have no effect on the human body.

Extra-low-frequency electromagnetic fields only affect electronic devices, not the human body.

When a human body is exposed to extra-low-frequency electromagnetic fields, it acts as a conducting medium, inducing electric fields and currents within the body.

Explanation

When a human body is exposed to extra-low-frequency electromagnetic fields, it acts as a conducting medium, inducing electric fields and currents within the body.

9. Derive the formula for the emf induced in a straight conductor moving in a magnetic field.

𝑒=𝐼𝐵

𝑒=𝐵𝑙𝑣

See image.

𝑒=𝑙𝐼

The correct formula for the emf induced in a straight conductor moving in a magnetic field is given by Faraday's Law of Electromagnetic Induction. The formula is not as simple as directly multiplying the quantities 𝐵, 𝑙, and 𝑣 or 𝐼, 𝐵, or 𝑙 with the induced emf 𝑒.

Explanation

The correct formula for the emf induced in a straight conductor moving in a magnetic field is given by Faraday's Law of Electromagnetic Induction. The formula is not as simple as directly multiplying the quantities 𝐵, 𝑙, and 𝑣 or 𝐼, 𝐵, or 𝑙 with the induced emf 𝑒.

10. Describe the production of an induced emf by a time changing magnetic flux

Induced emf can only be created by direct contact with a magnetic field

See image. A time changing magnetic flux will induce an emf in a circuit or coil (conductor).

A time changing magnetic flux will not induce an emf in a circuit or coil

An induced emf is produced by a stationary magnetic flux

When there is a time changing magnetic flux through a circuit or coil, Faraday's law of electromagnetic induction states that an emf is induced in that circuit or coil. This phenomena allows for the generation of electrical power in devices like generators.

Explanation

When there is a time changing magnetic flux through a circuit or coil, Faraday's law of electromagnetic induction states that an emf is induced in that circuit or coil. This phenomena allows for the generation of electrical power in devices like generators.

11. Describe the operation of an ideal transformer.

An ideal transformer can operate without any magnetic core material.

A transformer is a device that converts electrical energy into mechanical energy.

Transformers only work with direct current (DC) electrical systems.

See image.

An ideal transformer efficiently transfers electrical energy between circuits using electromagnetic induction, typically consisting of two coils wound around a core. It does not convert energy into mechanical form and requires a magnetic core for proper operation. Transformers are commonly used in alternating current (AC) systems.

Explanation

An ideal transformer efficiently transfers electrical energy between circuits using electromagnetic induction, typically consisting of two coils wound around a core. It does not convert energy into mechanical form and requires a magnetic core for proper operation. Transformers are commonly used in alternating current (AC) systems.