The energy carried by the incident light is
where h is the Planck constant and f is the frequency of the light. The threshold frequency is the frequency that corresponds to the minimum energy needed to eject the electrons from the metal, so if we substitute the threshold frequency in the formula, we get the minimum energy the light must have to eject the electrons:
Answer:
W= 4.4 J
Explanation
Elastic potential energy theory
If we have a spring of constant K to which a force F that produces a Δx deformation is applied, we apply Hooke's law:
F=K*x Formula (1): The force F applied to the spring is proportional to the deformation x of the spring.
As the force is variable to calculate the work we define an average force
Formula (2)
Ff: final force
Fi: initial force
The work done on the spring is :
W = Fa*Δx
Fa : average force
Δx : displacement
:Formula (3)
: final deformation
:initial deformation
Problem development
We calculate Ff and Fi , applying formula (1) :
We calculate average force applying formula (2):
We calculate the work done on the spring applying formula (3) : :
W= 11N*(0.7m-0.3m) = 11N*0.4m=4.4 N*m = 4.4 Joule = 4.4 J
Work done in stages
Work is the change of elastic potential energy (ΔEp)
W=ΔEp
ΔEp= Epf-Epi
Epf= final potential energy
Epi=initial potential energy
W=ΔEp= 5.39 J-0.99 J = 4.4J
:
68% So 68/100 of freshwater is found in ice
6. B. 4 electrons
7. Carbon is in everything and it's a compound that all organisms need
8. D. 3
9. Nitrogen gas is almost 80% of the atmosphere
10. Diatomic molecules compose 2 atoms
Answer:
Explanation:
a )
current in the wire = potential diff / resistance
= 23 / (15 x 10⁻³ )
= 1.533 x 10³ A .
b )
For resistance of a wire , the formula is
R = ρ L / S where ρ is specific resistance , L is length and S is cross sectional area of wire
putting the given values
15 x 10⁻³ = 4ρ / π x .003²
ρ = 106 x 10⁻⁹ ohm. m
= 10.6 x 10⁻⁸ ohm m
The metal wire appears to be platinum .
