## IB Physics Glossary

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### M

#### Magnetic fields

are in the direction from North pole (N) to South Pole (S):

Like poles repel:

Unlike poles attract:

For a straight wire carrying a current I:

Use the right-hand-screw rule to find the direction of B-field

For a coil carrying a current I:

Looking into the coil

- if direction of current is anti-clockwise then the end of the coil is a North Pole (magnetic field lines exit)
- if direction of current is clockwise then the end of the coil is a South Pole (magnetic field lines enter)

For a solenoid carrying a current I:

Looking into the solenoid

- if direction of current is anti-clockwise then the end of the coil is a North Pole (magnetic field lines exit)
- if direction of current is clockwise then the end of the coil is a South Pole (magnetic field lines enter)

#### Magnetic flux

the product of magnetic flux density and area. (d)
 Keyword(s): 12.1

the product of magnetic flux and number of turn. (d)
 Keyword(s): 12.1

#### Magnetic force

acts on a moving charge or a current carrying conductor.

We use Fleming's left-hand-rule to find the direction of the magnetic force, given B and I:
Note: electron displacement is in the opposite direction to conventional current I. F, B and I are perpendicular to each other.

The magnetic force F acting on a charge q moving with velocity v, making an angle θ with the magnetic field of strength B is given by

$$F=q v B \sin \theta$$.

Only moving  charged particles making an angle θ with the magnetic field "feel" the magnetic force, ie. v ≠ 0 and q ≠ 0 and θ ≠ 0.

The magnetic force F acting on a current I flowing through a conductor of length L, making an angle θ with the magnetic field of strength B is given by

$$F= B I L \sin \theta$$.

Only current carrying conductors making an angle θ with the magnetic field "feel" the magnetic force, ie. I ≠ 0 and θ ≠ 0.

#### Magnetic force on parallel wires

carrying electrical currents I can be summarized below.

#### Magnetic force on wires

carrying electrical currents I can be summarized below.

#### Magnification

, M, is the ratio image size/object size, or

$$M=\frac{L^'}{L}=\sqrt{\frac{A^'}{A}}$$

A represents area, L size/height/length.
 Keyword(s): 14.2

#### Magnitude of magnetic field

is defined as

$$B=\frac{F}{I L \sin \theta}$$

where B is the magnitude of the magnetic field, F is the magnetic force, I is the current, L is the length of conductor and θ is the angle between the current-carrying conductor and the magnetic field.

or

$$B=\frac{F}{q v \sin \theta}$$

where B is the magnitude of the magnetic field, F is the magnetic force, q is the charge, v is the velocity, θ is the angle between the path of the charged particle and the magnetic field.

#### Malus' law

The light transmitted, I, by an analyzer with incident intensity I0, is given by $$I=I_0 \cos^2 \theta$$.

• When the analyzer is parallel to plane of polarization of incident light, then
$$\theta=0^{\circ}, 180^{\circ} \text{and }\cos^2\theta=1$$

maximum light intensity is tranmitted

When the analyzer is perpendicular to plane of polarization of incident light (ie. they are crossed), then

$$\theta=90^{\circ}, 270^{\circ} \text{and }\cos^2\theta=0$$

zero light intensity is transmitted.
 Keyword(s): 4

#### Mass

is the amount of matter or substance inside an object.
Its value does not change with the strength of gravity. Identical objects on Earth and on the Moon have identical masses.
 Keyword(s): 2.2

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