Y10 Autumn Term Physics Roundup Flashcards
What is Current (I)?
- The flow of charge per second
- The charges that flow in a circuit are free electrons
- Electrons are pushed away from the negative terminal of the power supply + are pulled back towards the positive terminal
What’s current measured in?
Amperes (A)
What is the symbol for a switch?
1) A line sticking out with two circles on either side (open)
2) A straight line with two circles on either side (closed)
What is the symbol for a cell?
Two horizontal lines cut off by two vertical lines with a plus sign above one of them
What is the symbol for a battery?
Same as a cell but with two extra vertical lines w/ a dotted horizontal line in between them all in between the cell symbol
What is the symbol for a diode?
A straight line with an encircled pause button type thing in the middle of it
What is the symbol for a resistor?
A rectangle with two lines coming off either side
What is the symbol for a variable resistor?
Same as a normal resistor but with an arrow coming across it
What is the symbol for a LED (light emitting diode)?
Same as a regular diode but with two small arrows pointing away from it
What is the symbol for a lamp?
A circle with a cross inside of it and two line coming off on either side
What is the symbol for a fuse?
Same as a resistor but w/ a line going all the way through
What is the symbol for a voltmeter?
A circle with a V in it
What is the symbol for a ammeter?
A circle with an A in it
What is the symbol for a thermistor?
Same as a resistor but w/ an angled line going through it
What is the symbol for a LDR?
A smaller, encircled version of the resistor symbol with two arrows pointing towards it
What’s Potential Difference (V)?
The work done (energy transferred) per unit of charge that passes through a component
What’s potential difference measured in?
Volts (V)
What’s Resistance?
How easy/hard it is for electrons (current) to flow in a material
What’s resistance measured in?
Ohms
Give some examples of resistance in appliances
Filament lamp: higher temperature, higher R
Diode: forward resistance low, reverse resistance high
Thermistor: R decreases as temperature increases
LDR: R decreases as light intensity increases
What’s Ohm’s Law?
- The current through a resistor at a constant temperature is directly proportional to the p.d across it
- An Ohmic conductor gives an I-V graph that has a straight line through the origin
What’s an I-V graph/characteristic?
A graph of current against p.d for a component.
What are some examples of I-V graphs
- A resistor at constant temperature
- A filament bulb
- A diode
What’s a series circuit?
- A circuit where there is only one loop and one path for the current to take
- I is the same in each component
- Total p.d. is shared between components
- R is the sum of all the resistances of the components added together —> R total = R1 + R2
- Adding more resistors in series increases the total R as there is less I flowing in each resistor and the total p.d. stays the same.
What’s a parallel circuit?
- A circuit where there are two or more loops and therefore multiple paths the current can take.
- Total I is equal to the current in each component
- P.d across each component is the same
- Less current passes through resistors with bigger R
- The total R of two or more components in parallel is less than the resistor with the smallest R
- As we add more resistors in parallel, total R decreases as total I increases and total p.d. across them doesn’t change
What’s electric charge?
- Atoms are made up of a positively charged nucleus, surrounded by negatively charged electrons arranged in energy levels.
- Normally an atom has the same number of protons and electrons so has no overall charge
- If electrons are removed from an atom, it becomes positively charged
- If electrons are added to an atom, it becomes negatively charged
- A charged atom is called an ion.
What are charging insulators?
- Some insulating materials become charged when rubbed as electrons are transferred due to friction.
- To become positively charged, an insulating material loses electrons when rubbed
- To become negatively charged, an insulating material gains electrons when rubbed
What’s an electric field?
- A charged object has an electric field around itself. This is an area where the object will exert a force on another charged object.
- The force is a non-contact force
- Like charges repel
- Unlike (opposite) charges attract
What’s the equation for working out current?
Current (I) = Charge (Q) ÷ Time (t)
What are the equations for working out potential difference?
Potential difference (V) = Energy (E) ÷ Charge (Q)
or
Potential difference (V) = Current (I) x Resistance (R)
What’s direct current (d.c.)?
- Current that flows in one direction only in a circuit.
- Current from a battery is usually d.c.
What’s alternating current (a.c.)?
- Current that repeatedly flows in one direction then the other (reverses)
- Mains electricity is a.c.
- Mains a.c. has a frequency of 50 cycles per second or 50 Hz.
- Frequency of an a.c. —> supply = 1 ÷ the time taken for one cycle
What is the live wire?
- The brown wire in a plug
- In mains electricity, it carries a p.d. that alternates between -325V and +325V
What is the neutral wire?
- The blue wire in a plug
- Carries 0V p.d.
What is the earth wire?
- The green and yellow striped wire in a plug
- Connected to the longest pin
- Stops the metal case of an appliance becoming live
What’s a fuse?
- Melts if too much current passes through it which breaks the circuit
- A safety device
- Can be 3A, 5A or 13A depending on the appliance
- To decide what fuse to use, divide the power of the appliance by the p.d.
What’s Power (P)?
- The energy in Joules transferred to a device per second
- Measured in Watts, W
- Can be calculated in many different ways!
What’s Charge (Q)?
- The electrons that flow in a circuit
- Measured in Coulombs, C
- Charge flow through a resistor causes it to become hotter because the electrons collide with the ions in the resistor. The ions gain KE and so vibrate faster. This increases their thermal energy store.
Define electrical work
- The battery does work in a circuit to make the electrons move.
- The work done by the battery is equal to the energy transferred to the resistor
What’s an oscilloscope?
- A device that shows how an alternating p.d. changes with time.
- The Y-gain control changes how tall the waves are
- The time base control changes how many waves fit on the screen.
- The peak p.d. is the difference in volts between the highest and the middle level of the waves. If the p.d. of an a.c. Supply is higher, the waves (peak p.d.) get higher.
What’s the equation for working out energy?
Energy (E) = Charge (Q) x Potential Difference (V)
What’s the equation for working out charge?
Charge (Q)= Current (I) x Time (t)
What are the equations for working out power?
Power (P) = Energy (E) ÷ Time (t)
or
Power (P) = Current (I) x Potential Difference (V)
or
Power (P) = Current (I) [x2] x Resistance (R)
What are energy stores?
- Unit of energy is Joules, J
- Energy can be stored in a variety of different energy stores and can be transferred from one store to another:
- Chemical, kinetic, gravitational potential, elastic potential, thermal
What’s the Law of Conservation of Energy?
Energy cannot be created or destroyed
What happens to energy in a pendulum?
1) Max GPE as highest
2a) Min GPE as lowest
2b) Max KE as most GPE transferred to KE store
3) Max GPE as highest
What’s a closed system?
A system where no energy transfers take place into or out of the energy stores of the system.
What’s work?
Work is done on an object when a force causes the object to move
What’s the equation for energy and work?
Energy transferred = Work done
How does work react to friction?
- Work need to be done to overcome friction between objects.
- This is transferred as energy to the thermal energy stores of the objects that rub together and to the surroundings.
- Some examples of this are:
• Rubbing hands together
• Brake pads/discs
• Meteorites
How does Gravitational Potential Energy (GPE) work?
- Increases as an object is moved higher, decreases as an object is moved lower.
- Work is done on the object against the gravitational force acting on it to move it higher.
How does Kinetic Energy (KE) work?
- The energy an object has because it is moving
- Depends on the speed and mass of an object.
- Faster = more KE
- Heavier = more KE
How does Elastic Potential Energy (EPE) work?
- When work is done to stretch an elastic object, the energy is transferred to the EPE store of the object.
- Bigger extension (stretch) = more EPE stored - - Higher spring constant = more EPE stored
- EPE = 0.5 x spring constant x extension [2]
- Ee = 0.5 x k x e[2] (given in exam)
What’s the equation for work done?
Work Done (W) = Force (F) x Distance (s)
What’s the equation for Gravitational potential energy?
GPE (Ep) = Mass (m) x Gravitational Field Strength (g) x Height (Δh)
What’s the equation for Kinetic energy?
KE (Ek) = 0.5 x mass (m) x speed (v) [x2]
