physics

VALUE, UNCERTAINTY, UNIT ATOM STRUCTURE

  • Parts of an Atom:

    • Nucleus: Central part of an atom.

    • Protons:

      • Charge: +1

      • Contributes to the atomic mass.

    • Neutrons:

      • Charge: 0 (no charge)

      • Contributes to the atomic mass.

    • Electrons:

    • Charge: -1

    • Atoms are electrically neutral, containing an equal number of protons, neutrons, and electrons.

    • Protons and electrons cancel out their charges.

MODELS OF ATOM

  • Plum Pudding Model: Proposed structure of the atom.

  • Forces that keep the nucleus together:

    • Nuclear Forces:

    • Electrostatic Forces:

    • Strong Forces:

  • Charged Atoms:

    • Ion: Formed when an atom loses or gains electrons.

    • Loses electron: positively charged ion.

    • Gains electron: negatively charged ion.

ATOMIC STRUCTURE

  • Atomic Mass Number:

    • Example: Aluminium (Al)

    • Atomic Mass Number = 27 (sum of protons and neutrons).

    • Atomic Number = Number of Protons (e.g., for Al, it is 13).

    • Neutrons = Atomic Mass Number - Atomic Number (e.g., 27 - 13 = 14 neutrons).

    • For Al: 19 protons, 14 neutrons, 19 electrons.

  • Unstable Nuclei:

    • Some elements do not have the same number of protons and neutrons.

    • Rutherford Experiment Conclusions:

    1. Most of the atom is empty space.

    2. Nucleus is positively charged.

    3. Nucleus is very small.

ISOTOPES

  • Definition: Atoms of the same element with the same number of protons but different number of neutrons.

    • Example: Hydrogen has 3 isotopes.

    • Radioactive Isotopes:

    • Unstable nuclei that emit radiation.

    • Radioactive Decay: Process where unstable nuclei become more stable by causing emission of radiation.

    • Ionising Radiation: Radiation that can remove electrons from atoms.

TYPES OF RADIATION

  • Three Types:

    • Alpha (α):

    • Properties:

      • Positively charged.

      • Very large particles.

      • Cannot travel very far (stopped by paper).

      • Highly ionising due to larger size.

    • Beta (β):

    • Properties:

      • Negatively charged.

      • Moderately ionising.

      • Can travel for several meters in air.

      • Can be stopped by aluminium.

    • Gamma (γ):

    • Properties:

      • No charge, no mass.

      • Emitted following alpha or beta radiation.

      • Wavelengths of electromagnetic radiation.

      • Travels long distances in air.

      • Low ionising ability, stopped by lead.

HALF-LIFE

  • Definition: Time taken for the number of unstable nuclei of a particular isotope to halve.

    • Spontaneous and random; cannot be predicted but can be measured.

    • Example: For Carbon-14:

      • 1 Half-life = 5730 years.

      • Remaining percentages after subsequent half-lives:

      • 100% = 0 half-life (0 years)

      • 50% = 1 half-life (5730 years)

      • 25% = 2 half-lives (11460 years)

      • 12.5% = 3 half-lives (17190 years)

      • 6.25% = 4 half-lives (22920 years)

      • 3.12% = 5 half-lives (28650 years)

      • And so on, reducing by half each time.

NUCLEAR FISSION

  • Definition: Splitting of a heavy nucleus into two lighter nuclei.

    • Process:

    • A neutron is fired into a radioactive element (e.g., Uranium-235).

    • The unstable nucleus splits into daughter nuclei, releasing energy and additional neutrons (2 or 3).

    • This can lead to a chain reaction where the additional neutrons induce further fission events.

    • Part of the mass is converted to energy (E=mc2E=mc^2).

NUCLEAR FUSION

  • Definition: Combining lighter elements to form heavier elements along with the release of energy.

    • Example: Hydrogen isotopes combining to form Helium under high pressure and high temperature, overcoming the electrostatic forces between nuclei.

STATIC ELECTRICITY

  • Definition: Transfer of electrons due to friction between two objects (typically insulators).

    • Static electricity is stored in one place on the object.

ELECTRIC CHARGES

  • Types of Charge:

    • Positive Charge (+):

    • Negative Charge (-):

  • Electric Force:

    • The force between two charges can either repel or attract.

  • Electric Field:

    • Any region in space where a charge experiences a force.

ELECTRIC CURRENT AND RESISTANCE

  • Electric Current (I):

    • Flow of electrical charge.

    • Unit: Ampere (A).

  • Potential Difference (Voltage):

    • The driving force that pushes charges/electrons to move.

    • Unit: Volts (V).

  • Resistance (R):

    • Anything that slows the flow of current.

    • Unit: Ohm (Ω).

CHARGE

  • Definition: Measured in Coulombs (C), it represents the charge passing through a point in a circuit when a current of 1 ampere flows for 1 second.

ELECTRIC CIRCUIT SYMBOLS

  • Devices:

    • Ammeter:

    • Measures current in the circuit, connected in series.

    • Voltmeter:

    • Measures potential difference or voltage, connected in parallel.

RELATIONSHIPS IN ELECTRICITY

  • Ohm's Law:

    • As Voltage increases (R fixed), Current increases.

    • As Resistance increases (V fixed), Current decreases.

    • As Current increases (R fixed), Voltage increases.

SERIES AND PARALLEL CIRCUITS

  • Series Circuit:

    • Components connected in a single loop.

    • Current remains constant through all components.

    • Voltage divides among components.

  • Parallel Circuit:

    • Has multiple pathways/branches for current flow.

    • Voltage remains constant across all branches.

    • Current divides among branches based on resistance.

ELECTRIC POWER

  • Definition: Rate at which work is done or energy is transferred in a circuit.

  • Symbol: P

  • Unit: Watt (W).

  • Expression: Electric power can also be expressed in terms of charge transferred over time P = \frac{Q}{t} where Q is charge (C) and t is time (s).