The true length of a wire is $3.678 \,cm$. When the length of this wire is measured using instrument $A$,the length is $3.5 \,cm$. When the length of the wire is measured using instrument $B$,it is found to be $3.38 \,cm$. Then,the:

What is parallax? Explain the parallax method to measure the distance between the Earth and a planet.

$(a)$ The earth-moon distance is about $60$ earth radii. What will be the angular diameter of the earth (approximately in degrees) as seen from the moon?
$(b)$ The moon is seen to have an angular diameter of $(1/2)^{\circ}$ from the earth. What is its relative size compared to the earth?
$(c)$ From parallax measurement,the sun is found to be at a distance of about $400$ times the earth-moon distance. Estimate the ratio of sun-earth diameters.

How is time regulated in a wristwatch and a cesium clock?

$A$ man wishes to estimate the distance of a nearby tower from him. He stands at a point $A$ in front of the tower $C$ and spots a very distant object $O$ in line with $AC$. He then walks perpendicular to $AC$ up to $B$,a distance of $100 \; m$,and looks at $O$ and $C$ again. Since $O$ is very distant,the direction $BO$ is practically the same as $AO$; but he finds the line of sight of $C$ shifted from the original line of sight by an angle $\theta = 40^{\circ}$ ($\theta$ is known as 'parallax'). Estimate the distance (in $m$) of the tower $C$ from his original position $A$.

$A$ cuboidal block has dimensions $(1.5 \times 1.5 \times 1.0) \ cm$. What is the total surface area of the cuboid (in $cm^2$)?