Two wires of circular cross section are made of the same metal. Wire 1 has radius rr and length LL; wire 2 has radius 2r2r and length 2L2L. The potential difference between the ends of the wire is the same for both wires. Find the ratio of the resistance of wire 2 to the resistance of wire 1.

Ratio of wire 2 to wire 1 is 0.5 : 1

Explanation:

Wire 1:

length = L

radius = r

Wire 2:

length = 2L

radius = 2r

Resistance of a conductor varies directly as the length and inversely as the cross sectional area. Mathematically

l = length of conductor

a = cross sectional area of the conductor

p = resistivity of the material with which the conductor is made.

since we are considering the same material, we can ignore the resistivity of the wire.

For wire 1

cross sectional area =

therefore,

resistance R =

For the second wire 2

cross sectional area =

therefore,

resistance R =

Ratio of wire 2 to wire 1 will be

÷ = x

Ratio of resistance of wire 2 to wire 1 = 2/4 = 0.5 : 1

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.