El 2 Flashcards
Which direction does current flow?
From high voltage to lower voltage
how to reduce the energy lost as heat in cables
transmit energy at a very high voltage and low current
explain why the current is allowed to flow for a fixed length of time when verifying Joule’s law
the temperature rise of the water also depends on the time for which the current flows as well as the value of the current squared. therefore to investigate the relationship between temperature rise and current squared keep the time value constant
when verifying Joule’s law, give 2 other ways to reduce heat loss in the experiment
put an insulating lid on the calorimeter
do not allow the temperature of the water to get too high and this will reduce heat lost to the surrounding air
how would the IV graph for an ionic solution differ if its current was reduced
the slope would be reduced
describe how a micrometer is used 6
check for a zero error place the wire between the jaws (grips) tighten grip using slip control read main scale and vernier scale repeat at several points along the wire calculate an average value for this diameter
give 2 precautions to be taken when measuring the length of a wire
keep wire taut when measuring length
avoid error of parallax when measuring the length with a metre stick
explain why storage heaters have a large heat capacity
they take in a large amount of energy at night time (when it is cheaper) and release this large amount of energy slowly throughout the day
give a reason why the resistance of a filament bulb changes
as the current increases, the temperature of the filament increases, this causes increased thermal vibrations of the metal atoms, making it more difficult for the electrons to pass through the metal, the resistance increases
as the temperature increases, why does the resistance of a thermistor increase
as the temperature increases the number of electrons and holes (charge carriers) increases in the thermistor. More charge carriers means better conduction and therefore less resistance
what is an electric current
a flow of charge eg. a flow of electrons in a wire
explain why the resistance of a bulb is different when not connected to the mains
when not connected to the mians (bulb is off) the temperature of the filament is much lower. Since resistance of the filament depends on temperature, the lower temperature means a lower resistance
1 device other than a meter bridge to measure resistance and 1 advantage and 1 disadvantage
ohmmeter, portable, difficult to correct zero error
how is the risk of electrocution from a metal toaster minimised
the metal parts are earthed
explain, in terms of electrons, why light is emitted when a metal is heated
when the metal is heated the electrons gain energy (become excited).
electron jumps to a higher energy level
electron very quickly returns to lower energy level and a photon is emitted by the electron
