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Physics Chapter 12 : Topic 11
Forces Between Current-Carrying Conductors
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Magnetic flux through a surface is defined as:
Reasoning: Magnetic flux is the amount of magnetic field passing through a surface and is given by $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$ for an area perpendicular to the magnetic field.
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The SI unit of magnetic flux is:
Reasoning: Magnetic flux is measured in weber $\mathbf{(Wb)}$, where: $\mathbf{1\ Wb = 1\ T}\mathbf{m}^{\mathbf{2}}$.
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Magnetic flux depends on:
Reasoning: Magnetic flux is calculated by $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$.So, it depends on magnetic flux density and area.
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If the magnetic flux density through an area is doubled while area remains constant, the magnetic flux:
Reasoning: Since, $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$ $\Longrightarrow$ Doubling $\mathbf{(B)}$ doubles the magnetic flux.
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A surface has an area of $\mathbf{2}\mathbf{\ m}^{\mathbf{2}}$ and magnetic flux density is $\mathbf{3\ T}$. The magnetic flux through the surface is:
Reasoning: $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$ $\Longrightarrow$ $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= 3 \times 2 = 6\ Wb}$
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Magnetic flux is maximum when the surface is:
Reasoning: Maximum flux occurs when the magnetic field passes normally through the surface. $\Longrightarrow$ $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$
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If a surface is parallel to magnetic field lines, the magnetic flux through it is:
Reasoning: No magnetic field lines pass through the surface. $\Longrightarrow$ So, $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= 0}$
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The magnetic flux density is measured in:
Reasoning: Magnetic flux density $\mathbf{(B)}$ has $\mathbf{SI}$ unit tesla $\mathbf{(T)}$.
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One tesla is equivalent to:
Reasoning: $\mathbf{B =}$ $\frac{\mathbf{\Phi}_{\mathbf{B}}}{\mathbf{A}}$ $\Longrightarrow$ Therefore, $\mathbf{1\ T = 1\ Wb/}\mathbf{m}^{\mathbf{2}}$
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Magnetic flux is a scalar quantity because:
Reasoning: Magnetic flux has magnitude but no independent direction, so it is treated as a scalar quantity.
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If the area of a surface is increased while magnetic flux density remains constant, magnetic flux:
Reasoning: Magnetic flux is directly proportional to area. $\Longrightarrow$ $\mathbf{\Phi}_{\mathbf{B}}\mathbf{\propto A}$
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A magnetic field of $\mathbf{0.5\ T}$ passes normally through an area of $\mathbf{4\ }\mathbf{m}^{\mathbf{2}}$. The flux is:
Reasoning: $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA = 0.5 \times 4 = 2\ Wb}$
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The formula $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$ is valid when:
Reasoning: The given definition applies when the area is perpendicular to the magnetic flux density.
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Magnetic flux represents:
Reasoning: Magnetic flux measures the total magnetic field passing through a given area.
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A coil is placed in a uniform magnetic field. The magnetic flux through it will increase if:
Reasoning: Magnetic flux depends on area. $\Longrightarrow$ $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$Increasing area increases flux.
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If magnetic flux density becomes zero, the magnetic flux through any area becomes:
Reasoning: From, $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$ $\Longrightarrow$ If $\ \mathbf{B = 0}$, then $\ \mathbf{\Phi}_{\mathbf{B}}\mathbf{= 0}$.
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Magnetic flux density can be calculated from:
Reasoning: Rearranging $\mathbf{\ }\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$ gives $\mathbf{B =}$ $\frac{\mathbf{\Phi}_{\mathbf{B}}}{\mathbf{A}}$.
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If both magnetic flux density and area are tripled, the magnetic flux becomes:
Reasoning: $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$ $\Longrightarrow$ Tripling both gives $\mathbf{\Phi}_{\mathbf{B}}^{\mathbf{'}}\mathbf{=}\left( \mathbf{3B} \right)\left( \mathbf{3A} \right)\mathbf{= 9BA}$.
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Two identical surfaces are placed in the same magnetic field. Surface $\mathbf{A}$ is perpendicular and Surface $\mathbf{B}$ is parallel to the field. The ratio of flux through $\mathbf{A}$ to $\mathbf{B}$ is:
Reasoning: Surface $\mathbf{A}$ has maximum flux while surface $\mathbf{B}$ has zero flux.
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A magnetic flux of $\mathbf{10\ Wb}$ passes through an area of $\mathbf{5\ m}^{\mathbf{2}}$. The magnetic flux density is:
Reasoning: $\mathbf{B =}$ $\frac{\mathbf{\Phi}_{\mathbf{B}}}{\mathbf{A}}$ $\Longrightarrow$ $\mathbf{B =}$ $\frac{\mathbf{10}}{\mathbf{5}}\mathbf{= 2T}$
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The area used in calculating magnetic flux is the area:
Reasoning: Magnetic flux uses the effective area perpendicular to the magnetic field lines.
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A larger magnetic flux through a surface can be produced by:
Reasoning: Since $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$, increasing either $\mathbf{B}$ or $\mathbf{A}$ increases flux.
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Magnetic flux density is a measure of:
Reasoning: $\mathbf{B =}$ $\frac{\mathbf{\Phi}_{\mathbf{B}}}{\mathbf{A}}$ $\Longrightarrow$ It represents flux per unit area.
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A magnetic field passes through a surface at right angles. The magnetic flux is:
Reasoning: For perpendicular field $\Longrightarrow$ $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$
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Which statement about magnetic flux is correct?
Reasoning: Magnetic flux depends on both $\mathbf{(B)}$ and $\mathbf{(A)}$. $\Longrightarrow$ $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA}$
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If the cross-sectional area of a magnetic field region is reduced to half while $\mathbf{(B)}$ remains constant, magnetic flux:
Reasoning: Flux is directly proportional to area. $\Longrightarrow$ $\mathbf{\Phi}_{\mathbf{B}}\mathbf{\propto A}$
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A magnetic field of $\mathbf{4\ T}$ passes through an area of $\mathbf{0.25}\mathbf{\ m}^{\mathbf{2}}$. The magnetic fluxis:
Reasoning: $\mathbf{\Phi}_{\mathbf{B}}\mathbf{= BA = 4(0.25) = 1\ Wb}$
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Increasing the number of magnetic field lines passing through a surface indicates:
Reasoning: Magnetic flux represents the amount of magnetic field passing through an area ; more field lines mean greater flux.
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The dimensions of magnetic flux density are related to:
Reasoning: $\mathbf{B =}$ $\frac{\mathbf{\Phi}_{\mathbf{B}}}{\mathbf{A}}$
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The magnetic flux through a surface depends on the component of magnetic field:
Reasoning: Only the perpendicular component contributes to magnetic flux.
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