SU: 15
• How are power and focal length related?
a
Focal length is reciprocal of power
Focal length is reciprocal of the
square of power
C
Focal length is equal to power
d
None of the above

Focal length is reciprocal of power

Explanation:

The optical power the ability to either converge or diverge rays and it is inversely proportional to the focal length such that we express them as

where P is power and f is focal length. The unit of power is

normally called diopter D

For example, if the focal length is given as 10cm, we first convert it to meters by dividing by 100 hence f=0.1m then the power will be 1/0.1=10 D

Therefore, from the options given, Focal length is reciprocal of power or power is the reciprocal of focal length

d₁ = displacement of tern from arctic to antarctic = 11000 miles

d₂ = displacement of tern from antarctic to arctic =   - 11000 miles

d = total displacement for the journey

total displacement for the journey is given as

d = d₁ + d₂

d = 11000 + (-11000)

d = 0 miles

t₁ = time of travel from arctic to antarctic = 3 months = 3 x 30 days = 90 days

t₂ = time of travel from antarctic to arctic = 3 months = 3 x 30 days = 90 days

t = total time of travel

total time of travel is given as

t = t₁ + t₂

t = 90 + 90

t = 180 days

average velocity is given as

average velocity = total displacement/ total time

v = d/t

v = 0/180

v = 0 miles/day