light dependant resistors Flashcards
what is the symbol for a light dependant resistor?
what can a light dependant resistor also be called?
resistor with a ring around it and ARROWS pointing to it
An LDR
what is an ohmic conductor?
when the current through the resistor is directly proportional to the potential difference
(only if the temperature is constant)
when do LDR have a high resistance?
in dark conditions
in dark conditions, what is the resistance of an LDR like
high resistance
how is the resistance of the LDR in the light?
resistance is very low
when is the resistance of an LDR very low?
in the light
what can LDRs be useful for?
can be used to detect light
when on a call and the phone is to ur ear, the mobile phone turns off,
what is used to help save the battery by switching the screen off?
An LDR
what is the resistance like of an LDR when the phone is not held to ur ear?(in the light)
the resistance is very low, takes very little energy for the current to pass through the LDR
what does it mean for the resistance of a component to be low?
requires very little energy for the current to pass through the component
what else is low when the potential difference across the LDR is low?
the resistance
how is potential difference distributed between components in series?
it’s shared
they add up to the total PD leaving the cell
which component would have a larger potential difference when in series?
a lamp or a Light-dependant resistor?
A lamp
it lights up the screen
when a phone is held to ear during conversation, the LDR is in darkness. Explain the resistance of the LDR.
What does this lead to?
the resistance of the LDR rises sharply when in darkness
high resistance means a great deal of energy used for the current to pass through the LDR,
the pd across the LDR is very high meaning the pd of the lamp will be lower(less electrical energy is available for the lamp)
when the pd across a lamp is very low, what does this cause the lamp to be?
the lamp becomes very dim
