If a solid conducting cylinder was quickly inserted in a hole of the current-carrying pipe, it will not produce eddy currents because the field inside is zero. however, there is a magnetic in the outside of the current-carrying pipe, therefore, at entry/exist there is a magnetic field and the solid cylinder will experience eddy currents on the surface.

draw the following:

- the system

- the eddy currents

- the direction of velocity of the solid cylinder(at entry or exist)

- the direction of opposing force, would it effect the entry/exist velocity?

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.