OCR A A-Level Exploring Physics Experiments

OCR A A-Level Exploring Physics Experiments Demonstrating the photoelectric effect with the gold-leaf electroscope - correct answersMETHOD/OBSERVATIONS: -Charged rod is placed on top plate, repelling the gold leaf -When visible light or UV light is shone on a positively charged plate nothing happens, or if visible light is shone on a negatively charged plate -But if UV light is shone on a negatively charged zinc gold plate the gold leaf falls ANALYSIS: -The metal plate loses its negative charge through emission of electrons (not caused by air ions as electroscope is in vacuum) EXPLANATION: -Electrons are only emitted if the incident radiation is above the threshold frequency (UV light) -Emission of electrons starts as soon as the surface starts to be irradiated providing incident irradiation exceeds the threshold frequency - Not connected to intensity of light but wavelength Determining resistivity of a wire - correct answersMETHOD: -Take the current and p.d. for differennt lengths of wire -Measure the cross-sectional area of a wire using a micrometer ANALYSIS: -Calculate resistance and plot a graph of resistance (Y) vs length (X) -Gradient = R/L -Multiply gradient by cross-sectional area of wire (A) to give resistivity (p) -As p=RA/L REDUCING ERROR: -Measure the diameter at multiple places in case wire i