Radioactivity pt 2 and forces Flashcards
What is the activity of a radioactive source?
The number of unstable atoms in the source that decays per second. ( in Becquerels Bq)
What happens to the parent atom as the nucleus decays?
As the nucleus of each unstable atom decays, the number of parent atoms decreases. So the activity of the sample decreases.
What is count rate and how is it different to Activity?
Count rate is how much radioactivity you are detecting per second ( as picked up by a geiger counter) Whilst it is also measured in Becquerels, it is different to activity - which is the rate at which the unstable nucleus decays.
What is half life?
Half life is the average time taken for the count rate to fall by a half. ( this also means that at the value of half life, the number of nuclei have halved, the mass has halved and the count rate to half)
What are radioactive isotopes used for in medicine?
Medical imaging, treatments of cancer, tracers to monitor organs.
What two factors determine how useful a radioactive isotope is?
It’s half life and the type of radiation it emits. Should be medium length of half life and gamma radiation for medicine as it is more penetrative into the body. Cobalt has a half life of five years and it emits gamma radiation.
What is Nuclear fission?
The splitting of an atom’s nucleus into two smaller nuclei and the release of two or three neutrons and energy.
What is induced fission?
Induced fission occurs when a neutron is absorbed by a uranium-235 nucleus or a plutonium-239 nucleus and the nucleus splits. Spontaneous fission occurs without a neutron being absorbed.
How does a chain reaction in nuclear fission occur?
A chain reaction occurs in a nuclear reactor when each fission event causes further fission events.
How does a nuclear reactor control the number of neutrons undergoing fission?
Ina nuclear reactor, control rods absorb fission neutrons to ensure only one neutron per fission goes on to produce further fission.
What is nuclear fusion?
The process of forcing the nuclei of two atoms close enough together so that they form a single larger nucleus.
How is energy released in nuclear fusion?
Energy is released when two light nuclei are fused together. Nuclear fusion in the sun’s core releases energy.
What are the two practical conditions to consider when doing nuclear fusion?
A fusion reactor needs to be at a very high temperature before nuclear fusion can take place. The nuclei to be fused are difficult to contain.
What is radon gas?
An alpha emitting isotope that seeps into houses through the ground.
Why is nuclear waste hazardous?
It contains many isotopes that emit nuclear radiation for many years. The radiation is dangerous because it can cause cancer.
What is distance without change of direction?
Displacement
What is a Vector?
A vector quantity is something with magnitude and direction
What is a Scalar?
A quantity with magnitude but no direction
How is a Vector represented?
By an arrow in the direction of the vector and of length in proportion to the magnitude of the vector.
What is the ability of forces?
Forces can change the shape of an object, or change it’s motion or its state of rest. The unit of force is the Newton (N)
What is a contact force?
a force that acts on objects only when the objects touch each other.
What is Newton’s 3rd law of motion?
That when two objects interact, they always exert equal and opposite forces on each other.
What is the resultant force?
A single force with the same effect as all the forces acting on an object
If the resultant force is zero, what happens to the speed and direction of an object?
It stays the same. If resultant force is more than zero, there is a change in speed or direction.
If two forces act on an object along the same line, what happens to the resultant force?
The resultant force is the sum of the two forces if they are acting in the same direction, and their difference if they are acting in opposite directions.
What is a moment?
A measure of the turning effect of the force on an object.
What is the equation for moment?
M = F force x D distance
How do you increase the moment of a force?
Increase the force applied or the distance.
What can levers do?
They exert a force greater than the effort applied.
What is the pivot?
A measure of the turning effect of the force on an object. Pivot movements provide stability and support for rotation. The pivot of a force multiplier is nearer to the line of action of the force it exerts than to the force applied to it.
What can gears do?
Gears are used to change the moment of a turning effect. Low gear gives low speed and high turning effect. high gear gives high speed and a low turning effect.
How do you increase the moment of a turning effect?
To increase the moment of a turning effect, a small gear wheel needs to drive a larger gear wheel.
Explain why the turning force of a wheel nut is more than forces applied to a T bar
The turning force (moment) of a wheel nut is more because moment = force × distance. A T-bar increases the distance from the pivot point (the nut), so even with the same force applied, the larger distance creates a greater turning effect, making it easier to loosen or tighten the nut.
