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Questions and Answers
A wire carrying a current is placed perpendicular to a magnetic field. Which of the following changes will result in an increase in the force experienced by the wire?
A wire carrying a current is placed perpendicular to a magnetic field. Which of the following changes will result in an increase in the force experienced by the wire?
- Reducing the length of the wire within the magnetic field.
- Decreasing the magnitude of the magnetic flux density.
- Orienting the wire parallel to the magnetic field.
- Increasing the magnitude of the current flowing through the wire. (correct)
A positively charged particle moves perpendicularly into a uniform magnetic field. What is the shape of the path it will follow, and why?
A positively charged particle moves perpendicularly into a uniform magnetic field. What is the shape of the path it will follow, and why?
- A straight line, because the magnetic force does no work on the particle.
- A circle, because the magnetic force provides the centripetal force. (correct)
- A parabola, because the magnetic force acts like a constant acceleration.
- A spiral, because the magnetic force increases as the particle accelerates.
A rectangular coil with $N$ turns is placed in a uniform magnetic field $B$. The angle between the normal to the coil and the magnetic field is $\theta$. What is the formula for the magnetic flux linkage through the coil?
A rectangular coil with $N$ turns is placed in a uniform magnetic field $B$. The angle between the normal to the coil and the magnetic field is $\theta$. What is the formula for the magnetic flux linkage through the coil?
- $NBA\sin(\theta)$
- $BA\sin(\theta)$
- $NBA\cos(\theta)$ (correct)
- $BA\cos(\theta)$
A bar magnet is moved towards a coil of wire connected to a galvanometer. Which of the following actions will not increase the induced emf in the coil?
A bar magnet is moved towards a coil of wire connected to a galvanometer. Which of the following actions will not increase the induced emf in the coil?
A straight conductor is moved at a constant velocity through a uniform magnetic field, inducing an emf. According to Lenz's law, what is the direction of the induced current's magnetic field?
A straight conductor is moved at a constant velocity through a uniform magnetic field, inducing an emf. According to Lenz's law, what is the direction of the induced current's magnetic field?
A coil with 200 turns and an area of 0.05 m² is rotating uniformly in a magnetic field of 0.2 T at a frequency of 5 Hz. What is the maximum induced emf in the coil?
A coil with 200 turns and an area of 0.05 m² is rotating uniformly in a magnetic field of 0.2 T at a frequency of 5 Hz. What is the maximum induced emf in the coil?
Which of the following describes the effect of 'increasing the Y-gain' on an oscilloscope trace?
Which of the following describes the effect of 'increasing the Y-gain' on an oscilloscope trace?
An alternating current (AC) supply has a peak voltage of 170 V. What is the root mean square (rms) voltage of this AC supply?
An alternating current (AC) supply has a peak voltage of 170 V. What is the root mean square (rms) voltage of this AC supply?
What is the primary purpose of using transformers in the national grid?
What is the primary purpose of using transformers in the national grid?
A transformer has 500 turns in its primary coil and 100 turns in its secondary coil. If the primary voltage is 120 V, what is the secondary voltage, assuming an ideal transformer?
A transformer has 500 turns in its primary coil and 100 turns in its secondary coil. If the primary voltage is 120 V, what is the secondary voltage, assuming an ideal transformer?
What are eddy currents in a transformer core, and why are they undesirable?
What are eddy currents in a transformer core, and why are they undesirable?
A step-down transformer is used to reduce the voltage from 2400 V to 240 V. If the current in the secondary coil is 5 A, and the transformer is 90% efficient, what is the current in the primary coil?
A step-down transformer is used to reduce the voltage from 2400 V to 240 V. If the current in the secondary coil is 5 A, and the transformer is 90% efficient, what is the current in the primary coil?
Which of the following methods is commonly used to reduce energy losses due to eddy currents in a transformer core?
Which of the following methods is commonly used to reduce energy losses due to eddy currents in a transformer core?
A power transmission line carries 1000 A at 220 kV. If the resistance of the line is 0.1 ohms per kilometer, what is the power loss per kilometer due to resistive heating?
A power transmission line carries 1000 A at 220 kV. If the resistance of the line is 0.1 ohms per kilometer, what is the power loss per kilometer due to resistive heating?
A cyclotron accelerates charged particles using a magnetic field and an electric field. What is the role of the magnetic field in this process?
A cyclotron accelerates charged particles using a magnetic field and an electric field. What is the role of the magnetic field in this process?
Flashcards
Magnetic Field
Magnetic Field
A region around a magnet or current-carrying wire where a magnetic force is exerted.
Force on a Wire in a Magnetic Field
Force on a Wire in a Magnetic Field
The force on a current-carrying wire in a magnetic field is perpendicular to both the current and the magnetic field.
Left-Hand Rule
Left-Hand Rule
If a current-carrying conductor is placed in an external magnetic field, the conductor will experience a force perpendicular to both the conductor and the magnetic field.
Magnetic Flux Density (B)
Magnetic Flux Density (B)
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Force Equation on a Wire
Force Equation on a Wire
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Charged Particle in a Magnetic Field
Charged Particle in a Magnetic Field
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Force on a Moving Charge
Force on a Moving Charge
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Hall Probe
Hall Probe
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Mass Spectrometer
Mass Spectrometer
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Cyclotron
Cyclotron
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Magnetic Flux (Φ)
Magnetic Flux (Φ)
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Flux Linkage (NΦ)
Flux Linkage (NΦ)
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Electromagnetic Induction
Electromagnetic Induction
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Faraday's Law
Faraday's Law
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Lenz's Law
Lenz's Law
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Study Notes
- Magnetic fields arise from moving charges.
Magnetic Flux Density
- Describes what happens when current flows through a wire in a magnetic field.
- Fleming's left-hand rule applies to current-carrying wires in magnetic fields, determining the force direction.
- Magnetic flux density is measured in Tesla (T).
Force on a Wire in a Magnetic Field
- The equation F = BIl calculates the force on a current-carrying wire perpendicular to a magnetic field (B), where I is the current and l is the length of the wire.
- Experiments using a top pan balance determine how current, flux density, and wire length affect the magnetic force.
Charged Particles in Magnetic Fields
- Force direction on positive and negative charged particles moving through a magnetic field can be determined.
- A charged particle moving perpendicular to a uniform magnetic field follows a trajectory.
- The equation F = BQv calculates the force on a charged particle moving with velocity (v) perpendicular to a magnetic field (B), where Q is the charge.
Applications
- Hall probes utilize the force on moving charges in magnetic fields.
- Mass spectrometers and cyclotrons use magnetic force on charged particles.
- Cyclotrons and similar accelerators accelerate charged particles using magnetic fields.
Magnetic Flux and Flux Linkage
- Magnetic flux (Φ) is calculated as Φ = BA, where B is the magnetic flux density and A is the area when B is perpendicular to A.
- Flux linkage is the product of magnetic flux and the number of turns (N) in a coil: Flux linkage = NΦ.
- For rectangular coils not normal to B, magnetic flux and flux linkage can still be calculated, considering the angle.
Electromagnetic Induction
- Electromagnetic induction occurs when a conductor moves relative to a magnetic field or within a changing magnetic field.
- Faraday's law relates the induced electromotive force (EMF) to the rate of change of magnetic flux.
- Lenz's law dictates the direction of the induced EMF, opposing the change that caused it.
Applications of Electromagnetic Induction
- Lenz's and Faraday's laws apply to straight conductors cutting through magnetic fields and magnets spinning near coils.
- EMF calculations are performed for straight conductors or rectangular coils moving perpendicular to magnetic fields.
- Lenz's and Faraday's laws apply to coils rotating in magnetic fields.
- The induced EMF in a uniformly rotating coil varies.
- The peak induced EMF for a rotating coil can be calculated.
- The induced EMF in a rotating coil is affected by several factors.
Alternating Currents and Oscilloscopes
- Peak and peak-to-peak voltages and currents are key parameters for alternating currents.
- Root mean square (RMS) values are calculated for AC supplies.
- Average power in AC circuits can be determined.
- Oscilloscopes display AC and DC waveforms and measure time intervals, frequencies, and peak-to-peak voltages.
- Oscilloscopes can investigate the effect of angles between search coils and magnetic fields.
Transformers
- Step-up transformers increase voltage; step-down transformers decrease voltage.
- Transformers work by electromagnetic induction, transferring energy between primary and secondary coils.
- The ideal transformer equation relates the number of turns to the voltage ratio between primary and secondary coils.
- Eddy currents are induced in the transformer core.
- Energy is lost in transformers due to eddy currents and other factors; lamination of the core reduces these losses.
- Calculations relate current and voltage in primary and secondary coils to transformer efficiency.
Power Transmission
- Transformers help transmit electrical power efficiently in the national grid.
- Power losses in the national grid's transmission can be calculated.
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