Physics class test T2 Grade 10

Diamond properties

1. colourless, transparent and sparkles when light falls on it

2. is very hard, each carbon is held in place by 4 strong covalent bonds

3. high melting and boiling point

4. cannot conduct electricity cuz there’s no ions or free electrons to act as charge carriers

Graphite

carbon atoms are found in layers or plates. atoms in each layer are covalently bonded to three other carbon atoms so that regular hexagonal pattern is formed in the same plane

graphite properties

1. gray black shiny soft solid

2. unlike diamond, slippery cuz layers can slide over each other

3. good conductor of electricity because of free electron

Properties of covalent compounds

1. simple covalent molecules have low melting and boiling points. weak IMF, small amount of energy is needed to overcome them

2. Covalent network structures have high melting and boiling points cuz IMF are strong. Lattice structures are strong but brittle cuz bonds are rigid and not flexible

3. Covalent structures are poor conductors of electricity and heat. They are insulators. no free electrons with exception of graphite.

Ionic structures

1. solids that are built up out of ions of opposite charges that result from the reaction between a metal and a non metal.

2. cations electrostatically attract the anions and bond together by strong electrostatic forces

Properties of ionic comounds

1. hard and brittle

2. ionic solids are soluble in water and form solutions called electrolytes. can conduct electricity

3. high melting and boiling points. alot of energy is needed to overcome ionic bonds

4. do not conduct electricity as solids

5. conducts electricity when melted and dissolved. free ions can carry charge

properties of metals

1. metallic glow: sea of free electrons reflects light

2. conductors of electricity when solid or melted

3. good heat conductors

4. shapeable: : atoms can slide over each other even though they’re strongly bound

5. high density: atoms densely packed together in metal lattice

Properties of EM radiation

1. transverse

2. speed of 3 × 10⁸ m.s^-1

3. can move through a vacuum/don’t need a medium to propagate but can

4. transfers energy

5. display same wave nature, diffraction and interference

6. all obey the wave equation

Source of electromagnetic waves

acceleration of electrical charges. electrical charges in motion causes change in magnetic field. Around a changed magnetic field, a changed electrical field is formed. They are regenerating fields.

Propagation

Electromagnetic waves result from the accelaration of electric charges and are charcterised by an electric field induced perpendicular on changed magnetic fields

Penetrating ability of EM radiation

• The higher the frequency(the smaller the wavelength, the more energy the wave has.

• Some can penetrate skin or move through the body

• UV, X ray, gamma rays,

• Causes ionizing radiation which can break molecular bonds and create ions in the body

UV radiation and the skin

• UV can damage collagen fibres and thus speed up ageing of skin.

• As protection against UV radiation the body tans when exposed to moderate level of radiation by releasing the brown pigment melanin. helps block UV penetration and prevents damage to vulnerable tissue deep down

• sunscreen blocks partly against UVB and has an SPF to indicate protection against UVB radiation

UVA radiation

• UVA is least harmful but can age skin, damage DNA and possibly cause skin cancer.

• Penetrates skin and doesn’t cause sunburn

UVB radiation

• can cause skin cancer, radiation affects DNA molecules in skin cells resulting in possible cancerous mutations

• ozone layer in atmosphere protects us

• connection between UBV radiation and cancer is one of the reasons for concern of depleting ozone layer

What makes a good sunscreen?

• UVB protection: padimate O, Homosalate, Octisalate, Octinoxate

• UVA protection: Avobenzone

• both: Octocrylene, titanium dioxide, zinc oxide, Mexoryl

UV radiation and the eyes

• can damage eyes and lead to welders flash which can cause caaracts etc.

• Full coverage Protective eyewear for those exposed to UV

• plastic lenses > glass

• contacts protect retina y absorbing UV radiation

Gamma rays

• Because gamma rays have high energy levels, they can cause serous damage when absorbed by living cells.

• Not stopped by the skin and can change DNA by interference with genetic material of the cell

• DNA double helix breakage is generally accepted as the most biological significant legion causing cancer and hereditary disease by ionizing radiation

Cell phones and micro-radiation

• minimize radiation with use of hands-free kit to minimize radiation to the brain

• keep cell phones away from body

• don’t use cell phone in a car without external antenna

Particle nature of EM radiation

• Quantum – indivisible amount of a physical quantity (integer number)

• A photon is a quantum of EM radiation (packet of energy) and transfers the energy to particles of matter

• Zero mass

• Travels at the speed of light

• Refers to the particle nature of EM waves