Download 2015 Q10 - Loreto Balbriggan

State Examination Commission – Physics Higher Level, 2015
Question 10
There are about a trillion neutrinos from the Sun passing through your hand every second.
Neutrinos are fundamental particles and are members of the lepton family.
Leptons are not subject to the strong nuclear force.
What is the principal force that neutrinos experience?
Electrons are also members of the lepton family. Name two other leptons.
Name one fundamental particle that is subject to the strong nuclear force.
(12)
Pauli proposed that a neutrino is emitted during beta-decay.
Why did he make this proposal?
During beta-decay, a neutron decays with the emission of a proton, an electron and a neutrino.
Write a nuclear equation to represent beta-decay.
Calculate the energy released, in MeV, during beta-decay.
(26)
An electron can be detected in a cloud chamber. However it is much more difficult to detect a neutrino. Explain why.
In a cloud chamber an electron travels perpendicular to the direction of a magnetic field of flux density 90 mT and it
follows a circular path. Calculate the radius of the circle when the electron has a speed of 1.45 × 108 m s–1.
Describe the path of a neutrino in the same magnetic field.
(18)
______________________________________________________________
What is the principal force that neutrinos experience?
The weak force
Electrons are also members of the lepton family. Name two other leptons.
Positron & Muon
Name one fundamental particle that is subject to the strong nuclear force.
(12)
Up quark
Pauli proposed that a neutrino is emitted during beta-decay.
Why did he make this proposal?
It appeared energy and momentum were not conserved; his proposal corrected that.
During beta-decay, a neutron decays with the emission of a proton, an electron and a neutrino.
Write a nuclear equation to represent beta-decay.
1 n → 1 p + 0 β + ν̄
0
1
−1
Calculate the energy released, in MeV, during beta-decay.
Mass defect, m = 1.67492×10−27 -1.67262 ×10-27 - 9.10938 × 10-31
(26)
= 1.6749 x 1022 kg
E = mc2 = 1.25 x 1013 J = 0.78 MeV
An electron can be detected in a cloud chamber. However it is much more difficult to detect a neutrino. Explain why.
They are uncharged, have barely any mass and only interact very weakly with matter.
P.T.O
C. Garvey 2015
In a cloud chamber an electron travels perpendicular to the direction of a magnetic field of flux density 90 mT and it
follows a circular path. Calculate the radius of the circle when the electron has a speed of 1.45 × 108 m s–1.
Describe the path of a neutrino in the same magnetic field.
(18)
centripetal force = magnetic force
2
mv
= Bev
r
mv
9.1×10−31 ×1.45×108
−3
r =
=
= 9.2×10 m
−2
−19
Be
9.0×10 ×1.6×10
A neutron will move in a straight line as uncharged particles experienced no force in a magnetic field.