Unit 2 Flashcards
What effect does a higher capacitance have on the rate of charge/discharge
- increases time taken to charge
- longer for charge to build up on plates
Explain forward bias in terms of bands
- voltage from supply lowers energy of conduction band
- raises energy of valence band
- less work is done
What is e.m.f
The work done in moving each coulomb of charge in the circuit
What is a.c
Alternating current
- negative charges move back and forth
- changes direction
What happens if the timebase is halved
There will be have as many waves as before on the screen
When is a Wheatstone bridge circuit balanced
When the voltmeter reads zero
When is a Wheatstone bridge circuit out-of-balance
When the voltmeter doesn’t read zero
What band is full in an insulator
Valance band (lower band)
How can a diode be reversed biased
N-type connected to positive terminals. No conduction occurs
How can a diode be forward biased
N-type connected to negative terminals. Conduction occurs
What is added to give a p-type
Indium
What is added to give a n-type
Arsenic
What is a semiconductor
Insulating material that has been doped with an impurity to increase its conductivity
What effect will heating a semiconductor have
Resistance will decrease
What effect does a higher resistance have on the rate of charge/discharge
- increases time taken to charge
- decreases current
- decreases rate at which charges flow onto capacitor plates
Draw a graph of current against time for charging/discharging
(See notes for graph)
If resistance is increased across a resistor, what happens to the voltage and the current in the resistor
- voltage increases
- current decreases
How would internal resistance and e.m.f be found from a voltage/current graph
Gradient = -r Y-intercept = e.m.f
How would internal resistance and e.m.f be found from a resistance current graph
Gradient = e.m.f Y-intercept = -r
What is d.c
Direct current
- flows in one direction
- negative to positive
When can e.m.f be measured
When there is no current flowing
What is a capacitor
An electrical component that can store charge and therefore energy
What is capacitance
The amount of charge stored per unit of potential difference
What is internal resistance
The resistance of electrical source due to moving charges
Explain reverse bias in terms of bands
- voltage of supply will raise energy of conduction band
- lower energy of valence band
- more work is done
How would the internal resistance of the cell be found
Voltmeter connected across the terminals of the cell
What happens when a capacitor charges
- voltage will increase until it equals supply voltage
- current starts from maximum and decreases from zero
- due to voltage increasing to supply
Draw a graph of p.d against time for charging/discharging across resistors
(see notes for graph)
Draw a graph of potential difference against time for charging/discharging a capacitor
(See notes for graph)
How would you calculate Vreading on voltmeter on an out-of-balanced Wheatstone circuit
- V1 = R1/R1+R2 x Vs
- V3 = R3/R3+R4 x Vs
- Vreading = V1 - V3
What is lost volts
The potential difference used by the internal resistance
What is current
The amount of charge flowing per second
How is voltage found from a line on an oscilloscope
V = number of vertical divisions for amplitude x y-gain
How is the period of a wave calculated from an oscilloscope reading
T = number of horizontal divisions for one wavelength x timebase setting
Why might components get damaged
If the peak supply voltage is greater than the average voltage
Describe the difference for current in a series and parallel circuit
Series - equal
Parallel - current total = sum of current components
Describe the difference in voltage for a series and parallel circuit
Series - vtotal = v1 = v2 + v3
Parallel - voltage equal
What is resistance
The opposition to electrical current
When is the resistance largest in a circuit
When connected in series
What is power
The amount of energy transferred per second
What is internal resistance
Resistance of the electrical source (battery) due to moving charges
What is a p-n junction diode
An electrical component that is made of two types of semiconductor
What type of charges does the n-type lose
Negative charge carriers
What creates the depletion layer
The p-type losing positive charge carriers and the n-type losing negative charge carriers
In what direction (relating to the circuit symbol for a p-n diode) can the electrons flow
Against the direction of the arrow
What band is partially filled in the n-type semiconductor
Conduction band
