phy5 - fields question..free body force diagram Watch

old_skool
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#1
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can somebody help me with this question..i don't understand..

A speck of dust has a mass of 1.0 × 10-18 kg and carries a charge equal to that of one electron. Near to the Earth’s surface it experiences a uniform downward electric field of strength 100 N C-1 and a uniform gravitational field of strength 9.8 N kg-1.

Draw a free-body force diagram for the speck of dust. Label the forces clearly.



The diagram is basically..gravitational force acting downwards on the dust...and electric force acting upwards

why does electric force act upwards? it says in the question uniform downward electric field so surely it acts downwards too?
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Artemidoros.
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is that in examwizard?? i was puzzled by that as well.

I think it experiences an upward electrical force as it is negatively charged, and hence negative to positive?? :s:
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_MaThs_
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Electric field strength is the electric force exerted on each POSITIVE charge.... like Artemidoros said electron is negatively charged, we know a negatively charged particle- the electric field will be going OUTWARD towards the negative charge.

I hope this makes sense
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pow1990
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If its a downwards electric field, its from positive charge on top to negative charge on bottom. So if the electron is negatively charged it would be attracted upwards to the positively charged part of the field.

NB electric field is always positive to negative direction
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old_skool
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(Original post by Artemidoros.)
is that in examwizard?? i was puzzled by that as well.

I think it experiences an upward electrical force as it is negatively charged, and hence negative to positive?? :s:
yea its from examwizard...i don't understand it
what do u mean negative to positive?
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old_skool
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k thanks i get it now cheers
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