Do sacs get cross-mark by different teachers or just your own teacher?
depends on the school. usually no, for consistency i dont think they do.
Is this really so bad?
i wouldnt say so! unless you have copied off stuff, for example, from the following:
"Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV. It is named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the colour violet. These frequencies are invisible to humans, but visible to a number of insects and birds. They are also indirectly visible, by causing fluorescent materials to glow with visible light.
UV light is found in sunlight and is emitted by electric arcs and specialized lights such as black lights. It can cause chemical reactions, and causes many substances to glow or fluoresce. Most ultraviolet is classified as non-ionizing radiation. The higher energies of the ultraviolet spectrum from wavelengths about 10 nm to 120 nm ('extreme' ultraviolet) are ionizing, but this type of ultraviolet in sunlight is blocked by normal dioxygen in air, and does not reach the ground.[1] However, the entire spectrum of ultraviolet radiation has some of the biological features of ionizing radiation, in doing far more damage to many molecules in biological systems than is accounted for by simple heating effects (an example is sunburn). These properties derive from the ultraviolet photon's power to alter chemical bonds in molecules, even without having enough energy to ionize atoms.
Although ultraviolet radiation is invisible to the human eye, most people are aware of the effects of UV through sunburn, and in tanning beds. A great deal (>97%) of mid-range ultraviolet (almost all UV above 280 nm and most above 315 nm) is blocked by the ozone layer, and would cause much damage to living organisms if it penetrated the atmosphere. What remains of ultraviolet in sunlight after atmospheric filtering is responsible for the formation of vitamin D (peak production occurring between 295 and 297 nm) in all organisms that make this vitamin (including humans). The UV spectrum thus has many effects, both beneficial and damaging, to human health."
into your prac report:
Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV.These frequencies are invisible to humans, but visible to a number of insects and birds.UV light is found in sunlight and is emitted by electric arcs and specialized lights such as black lights.However, the entire spectrum of ultraviolet radiation has some of the biological features of ionizing radiation, in doing far more damage to many molecules in biological systems than is accounted for by simple heating effects (an example is sunburn). A great deal (>97%) of mid-range ultraviolet (almost all UV above 280 nm and most above 315 nm) is blocked by the ozone layer, and would cause much damage to living organisms if it penetrated the atmosphere. The UV spectrum thus has many effects, both beneficial and damaging, to human health.", then that is proably bad :p but if you have just snipped off sentences like the one you said above, it seems fair enough..
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