Series and Parallel Circuits
- Series circuits
- Parallel circuits
Series Circuits
Components in series are connected along a single path running around the circuit.
Current, I: The same current flows through all the components, and through each point in the circuit.
Voltage, V: This is shared between the components. There is a higher voltage across components with a greater resistance.
Resistance, R: The total resistance of components in series is equal to the sum of their separate resistances.
Parallel Circuits
In a parallel circuit the path splits at some point. This means that some current flows one way, and some the other.
Current, I: Whenever a charge flows into one junction, the same amount must flow out of it. This means that the current through the whole circuit is the sum of the currents through each separate component.
Voltage, V: This is the same across all components that are in parallel with one another.
Impulse, Force and Momentum
- Force and momentum
- Impulse = change in momentum
- Force and impulse
- Examples
Force and Momentum
Physicists often say “momentum is conserved”. However, this is not always the case. It is only true of there is no external force acting.
If there is an external force acting on an object, then the momentum of that object is not conserved, it is changing.
Impulse = Change in Momentum
The word impulse means the change in momentum. In Physics, we use the greek symbol Δ (“Delta”) to mean “change in”, so
Δp = “change in momentum” = impulse
Force and Impulse
The external force acting on an object is related to the impulse given to the object by:
where
- F = force (Newtons, N)
- Δp = impulse = change in momentum (kgm/s or Ns)
- t = time (seconds, s)
Worked Examples
Huygens’ Principle and Wavefronts
- Huygens’ principle
- Diffraction and Reflection
- Refraction
Huygens’ Principle
Given that waves are caused by a source of disturbance, and that waves themselves cause disturbance as they propagate, Christiaan Huygens (1629-1695) treated waves along the principle that:
Every point on a wave may be considered as a point source disturbance, causing secondary waves that spread out evenly in all directions with a speed equal to the speed of propagation of the wave.
Diffraction and Reflection
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2)
3)
Refraction
Momentum and Collisions
- Conservation of momentum
- Collisions
- Explosions
Conservation of momentum
The conservation of energy is a very important thing in Physics. However, energy is not the only thing that is conserved.
Unless a force is acting, momentum is also conserved. This means that the total momentum before something happens will be equal to the total momentum after that thing happens.
Collisions: example A bus and a car are each travelling at 40mph, but in opposite directions. When they collide the car remains in contact with the bus, and they both continue at 15mph in the direction the bus was travelling. If the car’s mass is 2000kg, what is the mass of the bus?
Explosions: example A cannon, initially stationary, fires a 15kg cannonball at 200m/s. If the cannon itself has a mass of 1500kg, with what speed does it recoil?
IV Plots
- What are IV plots?
- What does the gradient tell us?
- Recognising curves
Momentum
- What is momentum?
- Applying formula
- Examples
Momentum is a measure of how hard it is to stop something: if an object has a lot of momentum, it will be hard to stop it; if its momentum is low, it will be easy.
How much momentum do the following things have? “Loads”, or “not much”?
Momentum Equation
- p = momentum,
or
- m = mass,
- v = velocity,
Worked Examples
- What is the momentum of a 70kg person running at 5m/s?
- How fast is that same person going if they have a momentum of 210Ns?
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