A convex lens is held over a piece of paper outdoors on a sunny day. When the paper is held 26 cm below the lens, the sunlight is focused on the paper and the paper ignites. What is the focal length of the lens?

The focal length of the lens is 26 cm

Explanation:

Focal length (f) of the lens is the distance between the lens and the image. It is also the distance between the lens axis and principal focus.

Applying lens formula;

where;

f is the focal length

di is the image distance

do is the object distance

The object distance in this question is the distance of the sun from the lens, this distance is too large, and its inverse is infinitesimal.

The equation above will reduce to;

given;

di = 26 cm

Therefore, the focal length of the lens is 26 cm

answer: the correct answer is 1.

explanation: there are various process in which a radioactive nuclei decays:

1) alpha decay: in this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. the mass number is reduced by 4 units.

2) electron capture: in this decay process, a parent nuclei absorbs an electron and gets converted into a neutron. simply, a proton and an electron combines together to form a neutron. mass number does not change in this process.

3) gamma ray emission: it is a decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. this decay releases . this process does not change the mass number.

4) positron emission: it is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. this is also known as -decay. in this the mass number remains same.

from the above information, we see that only alpha-decay is producing a change in the mass number of the nucleus.

a person with a mass of 106kg has a weight of 1060n