Question

In large televisions, electrons are accelerated from rest by a potential difference of 20 kV and shot onto a phosphorescent screen to produce an image. What is the speed of the electrons when they reach the screen?
1.4 × 106 m/s
8.4 × 107 m/s
5.9 × 107 m/s
4.4 × 107 m/s
1.3 × 107 m/s

Answer 1

aplay work-energy theorem
ΔK=W(total)

Answer 2

in your case all other force are neglegible exept electric force

Answer 3

formula for Work involving ΔV=?

Answer 4

Using the energy-work theorem, q(V2-V1)+1/2*m*v^2=0
Since q=-1.6*10^(-19), V2-V1=20v, m=1.67*10^(-27)... and we're done

Answer 5

not exactly @Sothearith that gives V^2= - something !!!
ΔK=W(total)
K(final)-K(initial)= W(of electric force)
1/2*m*v^2 - 0= q*ΔV
1/2*m*v^2 = q*ΔV
and now we are done

Answer 6

alternative answer to same question:
"who cares i have a plasma TV"
:) :)

Answer 7

also 20KV=20,000 Volts

Answer 8

Oh I mean 20kv, anw @mos1635 i mentioned q=-1.6*10^(-19)c... Since electrons have negative charge, they move from lower potential to higher potential..

Answer 9

you are SO wrigt
i meesed the (-)
glad to be corrected.

Answer 10

i guess
eV = 1/2 mv^2
for non-relativistic approach