WorksheetsLearning Outcome (2 Hours) - Magnetism
Total questions: 40
Worksheet time: 20mins
The principles of magnetism and its characteristics can be described as:
The force of attraction or repulsion between objects due to their magnetic fields, with properties such as poles, field lines, and the ability to attract certain metals.
The ability of all materials to conduct electricity equally well, regardless of their composition.
The process by which heat is transferred from one object to another through direct contact.
The tendency of objects to float in water due to differences in density.
A magnetic field is:
a region where a magnetic force can be detected
a type of electric current
a form of visible light
a kind of gravitational field
Define magnetomotive force (Fm) and provide its formula.
Magnetomotive force (Fm) is the force that drives magnetic flux through a magnetic circuit. Formula: Fm = N × I, where N is the number of turns and I is the current in amperes.
Magnetomotive force (Fm) is the force that opposes electric current in a conductor. Formula: Fm = V × R, where V is voltage and R is resistance.
Magnetomotive force (Fm) is the energy stored in a magnetic field. Formula: Fm = 1/2×L×I2 , where L is inductance and I is current.
Magnetomotive force (Fm) is the rate of change of magnetic flux. Formula: Fm = dΦ/dt, where Φ is magnetic flux and t is time.
Define reluctance and provide its formula.
Reluctance (S) is the opposition to the creation of magnetic flux in a magnetic circuit. Formula: S = l/(μA), where l is the length of the magnetic path, μ is the permeability, and A is the cross-sectional area.
Reluctance (S) is the measure of electrical resistance in a circuit. Formula: S = V/I, where V is voltage and I is current.
Reluctance (S) is the tendency of a material to conduct heat. Formula: S = Q/(kA), where Q is heat flow, k is thermal conductivity, and A is area.
Reluctance (S) is the ability of a material to store electric charge. Formula: S = Q/V, where Q is charge and V is voltage.
Define magnetic field strength (H) and provide its formula.
Magnetic field strength (H) is the magnetizing force applied to a material. Formula: H = Fm/l, where Fm is magnetomotive force and l is the length of the magnetic path.
Magnetic field strength (H) is the force experienced by a moving charge in a magnetic field. Formula: H = qvB, where q is charge, v is velocity, and B is magnetic flux density.
Magnetic field strength (H) is the total number of magnetic lines of force passing through a unit area. Formula: H = B/A, where B is magnetic flux and A is area.
Magnetic field strength (H) is the resistance offered by a material to the flow of magnetic flux. Formula: H = Rm × I, where Rm is magnetic reluctance and I is current.
Define flux density (B) and provide its formula.
Flux density (B) is the amount of magnetic flux passing through a unit area. Formula: B = Φ/A, where Φ is the magnetic flux and A is the area.
Flux density (B) is the amount of electric current passing through a unit area. Formula: B = I/A, where I is the current and A is the area.
Flux density (B) is the amount of force per unit area. Formula: B = F/A, where F is the force and A is the area.
Flux density (B) is the amount of charge per unit area. Formula: B = Q/A, where Q is the charge and A is the area.
Define permeability.
Permeability is the ability of a material to support the formation of a magnetic field within itself. Formula: μ = B/H, where B is flux density and H is magnetic field strength.
Permeability is the ability of a material to conduct electricity. Formula: μ = V/I, where V is voltage and I is current.
Permeability is the ability of a material to resist deformation under stress. Formula: μ = F/A, where F is force and A is area.
Permeability is the ability of a material to absorb heat. Formula: μ = Q/t, where Q is heat and t is time.
When freely suspended, a permanent magnet will position itself in which direction?
North and south direction
East and west direction
Up and down direction
Random direction
What are the lines shown around the bar magnet called? Fill in the blank: These lines are called _________.
Magnetic Field Lines
Electric Field Lines
Latitudinal Lines
Gravitational Field Lines
Fill in the blank: ________ are materials that could be attracted by a magnet.
Magnetic Materials
Plastic Materials
Wooden Materials
Glass Materials
Fill in the blank: ________ is the capability of a magnet to attract magnetic materials.
Magnetism
Electricity
Gravity
Friction
What is the unit of magnetic flux (ϕ)?
Tesla (T)
Weber (Wb)
Henry (H)
Ampere (A)
What is the cause of the existence of a magnetic flux in a magnetic circuit called?
Magnetomotive Force (m.m.f.), Fm
Electromotive Force (e.m.f.), Em
Resistance Force (r.f.), Rf
Inductive Force (i.f.), If
What does 'N' represent in the equation for Magnetomotive Force (m.m.f.), Fm?
Number of turns of a coil
Current from electric supply
Magnetic flux
Electromotive force
Explain why the unit of m.m.f is the same as the unit of current (Ampere).
Because m.m.f is defined as the product of current and number of turns, and its unit is Ampere.
Because m.m.f is measured in Volts, which is the same as current.
Because m.m.f is a type of resistance, and resistance is measured in Amperes.
Because m.m.f is always greater than current, so they share the same unit.
Calculate the m.m.f. of a magnetic circuit if 5A current flows through 500 turns coil of wire. The formula is m.m.f., Fm = I x N. The m.m.f. is ______ A.
2500 A
5000 A
1000 A
25 A
What is the ability of m.m.f. to produce flux over the length of the flux path called?
Magnetic field strength (H)
Magnetic flux density (B)
Permeability (μ)
Reluctance (R)
Calculate the magnetic field strength, H for a magnetic circuit when the m.m.f., Fm is 15 amp-turns and the length of flux path, l is 1.5 metres. What is the value of the magnetic field strength, H?
10 A/m
5 A/m
15 A/m
1 A/m
What is the equation for Magnetic Flux Density, B?
B = ϕ / A
B = A / ϕ
B = ϕ × A
B = ϕ + A
What is the unit of Magnetic Flux Density, B?
Newton
Tesla or Wb/m²
Joule
Ampere
Calculate the magnetic flux density, B for a magnetic circuit when 0.5 Wb amount of flux flows through an iron core with 0.5 mm² cross sectional area.
1 M.Tesla
0.5 M.Tesla
2 M.Tesla
0.25 M.Tesla
What is the value of the permeability of free space (μ₀)?
4π x 10⁻⁷ H/m
1.6 x 10⁻¹⁹ H/m
9.8 x 10⁻³ H/m
3 x 10⁸ H/m
What is the definition of reluctance (S) in a magnetic circuit?
The 'magnetic resistance' a magnetic circuit to the presence of magnetic flux.
The ability of a magnetic circuit to conduct electricity.
The measure of electrical resistance in a wire.
The force required to move a magnet through a circuit.
What is the equation for reluctance (S)?
S = Fm / Φ
S = Φ / Fm
S = Fm × Φ
S = Φ × Fm
Calculate the reluctance, S for a magnetic circuit where the m.m.f., Fm is 8.9 amp-turns and the flux (Φ) is 0.24 webers. Fill in the blank: The reluctance, S is _______ A/Wb.
37.083 A/Wb
0.027 A/Wb
2.67 A/Wb
21.25 A/Wb
What is the formula for reluctance (S) in terms of permeability and area?
S = 1 / (μ₀ μᵣ A)
S = μ₀ μᵣ A
S = μ₀ / (μᵣ A)
S = μᵣ / (μ₀ A)
What is the unit of reluctance?
Henry (H)
Ampere-Turns per Weber (AT/Wb)
Weber (Wb)
Tesla (T)
Determine the reluctance of a piece of mumetal of length 150mm and cross-sectional area 1800 mm² when the relative permeability is 4000.
16,580 A/Wb
1,658 A/Wb
165,800 A/Wb
8,290 A/Wb
Explain why silicon iron is preferred in transformer cores based on its B-H curve.
Because silicon iron has low hysteresis loss as shown by its B-H curve.
Because silicon iron has high electrical resistance as shown by its B-H curve.
Because silicon iron is cheaper than other materials as shown by its B-H curve.
Because silicon iron has a high saturation point as shown by its B-H curve.
A flux density of 1.2T is produced in a piece of cast steel by a magnetising force of 1250A/m. Find the relative permeability of the steel under these conditions.
0.96
1.2
800
960
Compare between electrical and magnetic quantities.
Electrical quantities involve electric charge and voltage, while magnetic quantities involve magnetic field and flux.
Electrical quantities involve only magnetic field, while magnetic quantities involve only electric charge.
Electrical quantities and magnetic quantities are exactly the same.
Electrical quantities involve magnetic flux, while magnetic quantities involve electric current.
Hysteresis and the hysteresis loop can be best described as:
The lag between input and output in a system, often shown as a loop on a graph.
The direct proportionality between input and output in a system.
The immediate response of output to input without any delay.
A system where output is always less than input.
What is the formula for the amount of flux (Φ) in a composite series magnetic circuit?
Φ = Fm / S_total
Φ = S_total / Fm
Φ = Fm × S_total
Φ = S_total × Φ
A closed magnetic circuit of cast steel contains a 6 cm long path of cross-sectional area 1 cm² and a 2 cm path of cross-sectional area 0.5 cm². A coil of 200 turns is wound around the 6 cm length of the circuit and a current of 0.4A flows. Determine the flux density in the 2 cm path, if the relative permeability of the cast steel is 750.
0.12 T
0.05 T
0.20 T
0.08 T
Calculate the flux density B in the 2 cm path using B=AΦ , where Φ=7.54×10−5 and A=0.5×10−4 . Fill in the blank: The flux density B is ______ T.
1.51 T
0.15 T
7.54 T
0.75 T
Fill in the blank: In a magnetic circuit, Flux (φ) is measured in _________. In an electric circuit, Current (I) is measured in _________.
Webers, Ampere
Teslas, Volts
Henrys, Ohms
Farads, Coulombs
Fill in the blank: In a magnetic circuit, Reluctivity is analogous to _________ in an electric circuit.
Resistivity
Conductivity
Permittivity
Capacitance
Which of the following statements is true for a magnetic circuit?
Flux does not actually flow in the magnetic circuit
Current flows in the magnetic circuit
Resistance remains constant in the magnetic circuit
Continuous expenditure of energy is needed to maintain flux
Ways could be used to determine the magnetic field direction?
Multimeter
Compass
LCR Meter
Right hand rule
Right hand screw rule
State the Lenz Law
When a conductor cut across a magnetic field (flux), an e.m.f (voltage) will be produced in the conductor.
The magnitude of the induced e.m.f. in any circuit is proportional to the rate of change of the magnetic flux linking the circuit.
The direction of an induced e.m.f. is always such that it tends to set up a current opposing the motion or the change of flux responsible for inducing that e.m.f.
An induced e.m.f. is set up whenever the magnetic field linking that circuit changes.
