## IB Physics Glossary

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### H

#### Hybrid vehicles

use electric motors with a petrol engine as back-up to provide additional power when necessary. Sophisticated computerized systems switch from the electric motor to the petrol engine and back as required.
 Keyword(s): 8.6

### I

#### Ideal gas

is a gas in which the molecules do not interact or the intermolecular forces can be neglected. (d)
The ideal gas equation is $PV=nRT$. Here we use absolute temperature, T, with unit Kelvin.
 Keyword(s): 3.2, 10.1

#### Impulse

is the change in momentum or the product of force and time: $\Delta p = F \times \Delta t$. (d)
Its unit is N s (or kg m s-1).
 Keyword(s): 2.2

#### Inclined plane

is used to show the forces acting on a block which rests, or moves, along the plane:

The component of the weight down the plane is

$m g \sin\theta$.

 Keyword(s): 2.2

#### Inelastic collisions

occur when the total kinetic energy of a system decreases.
 Keyword(s): 2.3

#### Insulator

a material that does not allow the flow of electric charge through it.

#### Internal energy

of a substance is the total potential energy and random kinetic energy of the molecules of the substance. (d)
 Keyword(s): 3.1, 10.1

#### Internal resistance

of a cell/battery is the effective additional resistance that is added to a circuit by the cell/battery. This is caused by the electrical energy generated by the chemical reactions inside the cell/ battery which is dissipated within the battery when a current flows:

$\epsilon = I (R + r)$,

where $\epsilon$ is the emf of the cell/battery, I is the current flowing through the circuit, R is the resistance of the circuit component(s) and r is the internal resistance of the cell/battery.

A graph of voltage/potential difference across external resistor (y-axis) against current flowing (x-axis) can be used to find
• the internal resistance, r = - gradient
• emf of cell/battery, $\epsilon$= y-intercept
 Keyword(s): 5.2

is radiation composed of particles that individually carry enough energy to liberate an electron from an atom thus ionizing it.

Taken from wikipedia.
 Keyword(s): 7.2

#### Isobaric process

takes place at constant pressure.

The 1st law of thermodynamics is

$Q=\Delta U + W$, and $W=P \Delta V$.
 Keyword(s): 10.2

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