Electric & Magnetic Fields

Category: Electric and Magnetic Fields

Electric Fields

1 / 13

Electric field originates at...

A positive charge

A negative charge

Either a positive or negative charge

Where there is zero charge

2 / 13

Coulomb's law states:

The closer the charges, the stronger the force between them.

The closer the charges, the weaker the force between them.

A point charge will always repel another point charge in a vacuum.

A point charge will always attract another point charge in a vacuum.

3 / 13

Calculate the force between a +3pC point charge and a +2.5pC point charge which are a distance of 3nm apart.

7.5x10³ N

7.5x10⁹ N

2.2x10¹⁰ N

2.2x10^-5 N

4 / 13

The force between two point charges has been calculated as -6.8x10⁴ Which of the following statement is correct?

The charges are alike and the force is repulsive.

The charges are opposite and the force is attractive.

The charges are opposite and the force is repulsive.

The charges are alike and the force is attractive.

5 / 13

Electric field strength...

Is a vector pointing in the direction a negative charge would move.

Is a vector pointing in the direction a positive charge would move.

Is a vector pointing in the direction a neutral charge would move.

Has no direction so cannot be a vector.

6 / 13

Which graph best represents the electric field strength of a radial field?

Graph A

Graph B

Graph C

Graph D

7 / 13

Calculate the electric field strength due to. point charge of 15.0 μm at a distance of 44 mm from the charge.

3.1x10⁶

3.0x10⁶

3.1x10³

3.0x10³

8 / 13

A uniform field can be produced by connecting...

Two adjacent plates to the same pole of a battery.

Two parallel plates to the same pole of a battery.

Two adjacent plates to opposite poles of a battery.

Two parallel plates to opposite poles of a battery.

9 / 13

Calculate potential difference of two plates that are 3 mm apart that are producing a field strength of 4x10⁵.

7500 V

12x10² V

1.2x10³ V

12x10^-2 V

10 / 13

In this equation, what does the "V" represent?

The electric potential energy that a unit positive charge would have at infinity.

The electric potential energy that a unit positive charge would have at a given point.

The electric potential energy that a unit negative charge would have at infinity.

The electric potential energy that a unit negative charge would have at a given point.

11 / 13

In the same equation, what is "Q" measured in?

NC^-1

Vm^-1

12 / 13

Equipotentials show...

All points of equal potential on a rugby field

All points of equal potential in a radial electric field

All points of equal potential in a uniform electric field

All point of equal potential in any electric field

13 / 13

A potential difference V is applied across two parallel plates. A particle exactly halfway between the two plates at point A experiences an electric force F. The electron moves to point B which is halfway between point A and the right-hand plate. Which of the following is the electric force experienced by the electron at Y? [image]

F/4

F/2

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Capacitors

1 / 16

What unit is capacitance measured in?

Coulombs²

Farads

Volts

Farquaads

2 / 16

A 300μF capacitor is charged fully to 3.2 μC, calculate the voltage of the battery that was used to charge the capacitor?

0.012 V

0.01 V

1.2 V

1 V

3 / 16

The p.d. across a capacitor is ________ to the charge stored on it.

opposite

inversely square

irrelevant

proportional

4 / 16

Which of these equations is not a correct expression of the energy stored by a capacitor?

Expression A

Expression B

Expression C

Expression D

5 / 16

Which graph best shows the charging of a capacitor?

Graph A

Graph B

Graph C

Graph D

6 / 16

Which graph best shows the discharging of a capacitor?

Graph A

Graph B

Graph C

Graph D

7 / 16

A 200 μF capacitor is charged fully to 1.6 μC, calculate the energy stored when it is fully charged.

1.25x10^-6 J

6x10^-9 J

8x10^-3 J

5.1x10^-4 J

8 / 16

A capacitor is charged fully to 300 nF with a battery of 0.5 V, calculate the energy stored when it is fully charged.

6x10¹¹ J

1.6x10⁶ J

3.7x10^-8 J

7.5x10^-8 J

9 / 16

A 200 μF capacitor is charged fully with a 3 V battery, calculate the energy stored when it is fully charged.

3x10^-4 J

0.003 J

0.015 J

6x10^-4 J

10 / 16

The potential difference across the plates of a capacitor is decreased by a half. There is no change to the capacitance of the capacitor. Which of the following statements is true?

The energy stored by the capacitor will reduce by half.

The energy stored by the capacitor will quadruple.

The energy stored by the capacitor will double.

The energy of the capacitor will reduce by a quarter.

11 / 16

A capacitor with capacitance C is charged to a potential difference of V. The energy stored on the charged capacitor is W. What would be the energy stored if the potential difference was 4V?

2 W

4 W

8 W

16 W

12 / 16

What piece of equipment could you use to measure and record the potential difference across the capacitor over time?

Datalogger and ammeter

Oscilloscope

Cathode ray tube

Lux Meter

13 / 16

The time taken to discharge (or charge) a capacitor depends on:

The capacitance of the capacitor.

The resistance of the circuit.

The capacitance of the capacitor and the resistance of the circuit.

None of the above.

14 / 16

In this equation to calculate the charge remaining on the capacitor, what does Q₀ represent?

The charge of the capacitor when it's fully charged.

The charge of the capacitor before it discharges.

The lowest amount of charge the capacitor can hold.

15 / 16

What is meant by the time constant of a resistor-capacitor circuit in terms of potential difference?

The time taken for the potential difference to decrease by 50%

The time taken for the for the potential difference to reduce by 37%

The time taken for the for the potential difference to reduce by 63%

The time taken for the for the potential difference to reduce by 100%

16 / 16

Which equation shows the natural log being taken of the discharge equation for charge?

Equation A

Equation B

Equation C

Equation D

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Magnetic Fields and Forces

1 / 13

Which way do magnetic field lines run?

Centre of magnet to North Pole

North Pole to South Pole

Centre of magnet to South Pole

South Pole to North Pole

2 / 13

Select the false statement:

The closer together the lines, the stronger the magnetic field.

The lines are closer together away from the poles.

The closer together the lines, the greater the force experienced in the field by a charged particle.

As the field lines get closer, they still will never cross.

3 / 13

Look at these diagrams, which current carrying wire will have the largest magnetic field?

Wire A

Wire B

Wire C

Can't tell from the image

4 / 13

Which diagram(s) have a magnetic field that has a clockwise direction?

Wire A

Wire B

Wire C

Wire A and B

5 / 13

Which diagram has the largest magnetic flux?

Wire A

Wire B

Wire C

Can't tell from the image

6 / 13

A current carrying wire is placed in a magnetic field as shown in this diagram. Which way is the resultant force acting?

7 / 13

The current is now reversed, which way is the resultant force now acting?

8 / 13

A 2.5N magnetic force acts on a 475m wire that is perpendicular to a 0.50 T magnetic field. Calculate the current in the wire.

0.008 A

0.011 A

0.016 A

0.023 A

9 / 13

There is a magnetic force of 2N on a 15 cm segment of wire carrying 4.5A. Calculate magnetic flux density?

0.03 T

1.35 T

2.96 T

29.6 T

10 / 13

In which diagram is no resultant force experienced?

11 / 13

A 23 cm wire carrying 3 mA of current is placed at an angle of 47° to the field lines of a uniform magnetic field of with a magnetic flux density of 0.75 T. Calculate the resultant force experienced by the wire.

4.1x10^-2 N

3.78 x10^-4 N

2.43x10^-2 N

3.52x10^-4 N

12 / 13

A wire has a radius of 2 mm, a mass of 14g and a density of 8960 kg m^-3 and carries a current of 2.5 A. Calculate the force experience by the wire when it is placed at right angles to a horizontal uniform magnetic field of flux density 4.3 x 10^-4 T.

17.5 N

1.33x10^-4 N

3.97 N

1.68x10^-5 N

13 / 13

An Alpha particle is travelling through a uniform magnetic field of flux density 4.3x10^-3 T at an angle of 32° to the field lines. There is a force of 1.76 x10^-15 N acting on the Alpha particle. Calculate the velocity of the Alpha particle.

2.4x10⁶ ms^-1

4.8x10⁶ ms^-1

4.1x10⁸ ms^-1

3.0x10⁸ ms^-1

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Electromagnetic Induction

1 / 10

Magnetic flux density is...

the area of a magnetic field

the strength of a magnetic field

a constant

2 / 10

How would you induce e.m.f in a flat coil?

Hold a magnet still in the coil.

Move a magnet in and out of the coil.

Hold a magnet still outside of the coil.

3 / 10

A coil with N turns has a flux density of B. What would be the flux density if you doubled the turns?

B/2

B^2

4 / 10

Calculate the magnetic flux passing through a coil of diameter 350 mm if the magnetic flux density is 240 mT and the angle between the normal to the plane of the coil and the direction of the magnetic field is 56°.

0.023 Wb

0.072 Wb

0.079 Wb

7.88x10⁷ Wb

5 / 10

Which statement describes Faraday's Law?

The induced e.m.f. is inversely proportional to the rate of change of flux linkage.

The induced e.m.f. is directly proportional to the rate of change of flux linkage.

The induced e.m.f. is always in a direction to oppose the change that causes it.

The induced e.m.f. is always in the same direction to the change that causes it.

6 / 10

A 40 cm metal rod moves through a uniform magnetic field in a perpendicular motion at a constant velocity of 0.24 ms^-1 for 15 seconds. The magnetic field has a magnetic flux density of 1.1 T. Calculate the the magnitude of the e.m.f induced.

1.584 V

0.322 V

0.106 V

0.483 V

7 / 10

A metal rod cuts Φ Wb of flux in 2 seconds and induces an e.m.f. of E. What would be the value of E if twice the flux was cut in a quarter of the time?

0.5E

8 / 10

Which statement describes Lenz's Law?

The induced e.m.f. is inversely proportional to the rate of change of flux linkage.

The induced e.m.f. is directly proportional to the rate of change of flux linkage.

The induced e.m.f. is always in a direction to oppose the change that causes it.

The induced e.m.f. is always in the same direction to the change that causes it.

9 / 10

Magnetic flux is...

Equal to the product of B and the number of turns in the coil placed within the magnetic field.

A scalar value, which represents the amount of B flowing through a cross-sectional area, bounded by a closed loop.

A vector field, indicating the strength of the magnetic field at a given point in a medium.

The strength of a magnetic field.

10 / 10

Magnetic flux linkage is...

Equal to the product of B and the number of turns in the coil placed within the magnetic field.

A scalar value, which represents the amount of B flowing through a cross-sectional area, bounded by a closed loop.

A vector field, indicating the strength of the magnetic field at a given point in a medium.

The strength of a magnetic field.

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Alternating Currents

1 / 10

What does AC stand for?

Actual Current

A Current

Alternating Current

Alternative Current

2 / 10

A step up transformer...

Increases the current

Increases the voltage

Increases the cost of producing electricity

3 / 10

A step down transformer...

Decreases the current

Decreases the voltage

Decreases the cost of producing electricity

4 / 10

What is the number of turns on the primary coil of a transformer if it's input voltage is 720V and it's output voltage is 245 V with 350 turns on the secondary coil?

252 turns

504 turns

1029 turns

2058 turns

5 / 10

What is the input current of a transformer if has 535 turns on it's primary coil and it's output current is 2.0 A with 50 turns on the secondary coil?

0.19 A

2.1 A

14.3 A

21.4 A

6 / 10

If a transformer has 400 turns on it's primary coil, and 200 turns on it's secondary coil it is...

A step up transformer

A step down transformer

7 / 10

The frequency of UK mains ac is 50 Hz, what is it's time period?

0.02 s

0.05 s

2 s

5 s

8 / 10

Using this diagram, which arrow is measuring the peak voltage?

9 / 10

A wire carries an alternating current of peak value 2 A. Calculate the root mean square value the current.

0.7 A

1.4 A

2 A

10 / 10

An ac supply has an V₀ value of 3 V and a root mean square current of 0.52 A. Calculate the root mean square power of the supply.

0.17 W

0.75 W

1.1 W

1.56 W

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