The surface area SSS, in mm2\text{mm}^2mm2, of a metallic crystal growing in a laboratory environment is monitored over time. The surface area is modelled by the equation
log10S=0.85+0.072t \log_{10} S = 0.85 + 0.072t log10S=0.85+0.072twhere t t\,t is the time in hours after the crystal began to form.
Use the equation of the model to answer parts (a) and (b).
Find the initial surface area of the crystal, giving your answer to 2 decimal places.
After T T\,T hours, the surface area reaches 120 mm2. Find the value of TTT, giving your answer to 2 decimal places.
104 exam-style questions on OCR A Level Maths 1.6 Exponentials and Logarithms, covering 1.6.1 Properties of the exponential function, 1.6.2 Gradient of e^(kx) (A-level only), 1.6.3 Definition of the logarithm, 1.6.4 The natural logarithm function, 1.6.5 ln x as inverse of e^x, 1.6.6 Laws of logarithms, 1.6.7 Equations involving exponentials, 1.6.8 Reduction to linear form, and 1.6.9 Modelling using exponential functions. Each one has a worked solution and a mark scheme showing where the marks go.