GCSE Physics A (Triple) OCR

This subject is broken down into 73 topics in 8 modules:

  1. Matter 10 topics
  2. Forces 16 topics
  3. Electricity 8 topics
  4. Magnetism 6 topics
  5. Waves in Matter 9 topics
  6. Radioactivity 10 topics
  7. Energy 6 topics
  8. Global Challenges 8 topics
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  • 8
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  • 73
    topics
  • 27,243
    words of revision content
  • 3+
    hours of audio lessons

This page was last modified on 28 September 2024.

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Physics A (Triple)

Matter

The History of the Atom

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The History of the Atom

The Early Models of the Atom

  • Democritus (460-370 BC) first introduced the concept of the atom, which he thought to be an indivisible unit from which everything was composed.
  • John Dalton (1803) introduced his atomic theory, suggesting that all matter is composed of atoms, which are indivisible and indestructible particles.
  • Dalton proposed that all atoms of a given element are identical in mass and properties.

Discovery of Sub-Atomic Particles

  • J.J. Thompson's experiments (1897) led to the discovery of electrons – very small, negatively charged particles present in an atom.
  • Thompson developed the "plum pudding" model of the atom, wherein negative electrons were embedded in a spread of positive charge, like plums in a pudding.
  • Rutherford’s alpha scattering experiment (1909) showed that most of the mass and positive charge is concentrated at the centre (the nucleus) of the atom.
  • This led to the development of the "nuclear model" of the atom.
  • Niels Bohr (1913) further improved this model by introducing energy levels or shells for electrons.
  • James Chadwick (1932) is credited with discovering the neutron – a neutral particle found in the nucleus along with protons (positively charged particles).

Modern Understanding of the Atom

  • Today, atoms are known to consist of a nucleus (containing protons and neutrons) and electrons.
  • Electrons move around the nucleus in energy levels or shells.
  • The number of protons (atomic number) identifies each element.
  • The total number of protons and neutrons (mass number) identifies each isotope of the element.

Key Concepts and Terminology

  • Isotopes: These are atoms of the same element (same number of protons) but with different numbers of neutrons (different mass numbers).
  • Ions: These are charged atoms or groups of atoms. They are formed when atoms lose or gain electrons.
  • Orbitals: These are regions of space where there is a high probability of finding an electron. They are grouped into energy levels or electron shells.

Make sure you have a thorough understanding of these concepts as they form the foundation of the atomic theory.

Course material for Physics A (Triple), module Matter, topic The History of the Atom

Physics A (Triple)

Magnetism

Motors and Loudspeakers

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Motors and Loudspeakers

Electric Motor

  • An electric motor uses the interaction between the magnetic field created by a current in the coil and a separate magnetic field to create rotation.
  • The coil of wire within the motor is referred to as an armature.
  • Two types of motors are direct current (DC) motor, and alternating current (AC) motor.
  • The force exerted on the coil of an electric motor is maximised when the plane of the coil is perpendicular to the magnetic field.
  • The direction of force on the motor can be determined by Fleming's Left-Hand Rule: thumb represents the motion (Force), first finger represents the field (Field) and second finger represents the current (Current).
  • The 'split-ring commutator' is a clever arrangement that reverses the current in the coil every half turn to ensure the torque is always in the same direction, keeping the motor spinning in one direction.
  • The process of continually reversing the current is also known as commutation.

Motor Effect

  • The motor effect is the force experienced by a current-carrying conductor in a magnetic field.
  • The size of the force increases with a stronger magnetic field, a larger current, and a greater length of wire within the magnetic field.
  • The motor effect is used in a range of applications such as electric cars, fans, drills and blenders.

Loudspeakers and Microphones

  • A loudspeaker works by converting electrical signals into sound waves. This is accomplished through the motor effect.
  • In a loudspeaker, the current in a coil of wire varies with the electrical signals from the sound source. This alternating current creates an alternating magnetic field which interacts with a permanent magnetic field causing the coil to move back and forth. This motion is transferred to the speaker cone, causing it to vibrate and create sound waves.
  • A microphone essentially works in the opposite way to a loudspeaker: it uses a diaphragm, attached to a coil of wire, that vibrates in response to sound waves. As the coil moves, it changes its position in relation to a permanent magnet. This motion induces an electrical signal in the coil, corresponding to the sound waves.

Remember, understanding the principles of electromagnetism will allow you to understand how many common electrical appliances function, such as motors or loudspeakers. Practice applying the principles and rules to gain a deeper understanding of the topic.

Course material for Physics A (Triple), module Magnetism, topic Motors and Loudspeakers

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